I need a semi-anonymous system that allows players to rat each other out

It might not fit your game needs, but the following mechanic seems like it might be interesting:

Components (players are identified with colours and/or icons):
A mixture of "non-rat" and "rat" cards. Both cards come in "identifiable" form (bearing the colour/icon of a player) and "anonymous" (plain) form. Probably, more rat cards are anonymous than identifiable, whereas non-rat cards are about 50% anonymous.

Setup:
Each player gets a shuffled pile of cards containing:
* all their identifiable player-specific cards, and
* some anonymous cards

Mechanic:
Players maintain a hand of cards. This hand can contain identifiable cards which can be traced back to them (since they bear that player's mark) and anonymous cards which can't (since they are plain).
When ratting occurs, each potential ratter plays a card and the cards are shuffled together. The potential rattee then reveals the top N cards (N will affect the probability of a rat action going undiscovered).
* If they are all non-rat card, no rats are discovered.
* If there are any rat cards, someone ratted! Reveal all the cards. Some players may be proved innocent, and some may be unmasked as rats (either directly or by a process of elimination). The rest will be "under suspicion". (Note that if more than one player rats, and the rest of the players identifiably non-rat, all the rats will be unmasked regardless of whether or not they ratted anonymously.)

Properties:
* Playing an identifiable non-rat card means that you will not fall under suspicion.
* Playing an anonymous non-rat card risks falling under suspicion if a rat is discovered. It also means that if someone else rats anonymously, nothing can be proved against them.
* Playing an identifiable rat card is risky, since if any rats are discovered then you will be unmasked.
* Playing an anonymous rat card means you will certainly be under suspicion if any rats are discovered, and you may even be unmasked.
* The only way for a rat to be discovered but remain unidentified is for someone else to play an anonymous non-rat card. (So there need to be enough of these to make the game interesting.)

Notes:
In a paranoiac theme, being "under suspicion" should probably carry some game penalty (although obviously not as much as being unmasked as a rat).

Okay. You want three outcomes:

"Zero result": Ratting doesn't have any consequences.
"Anon. Tattle": Ratting punishes the person being tattled on.
"Public Tattle": Ratting punishes the person being tattled on and reveals the tattler.

Of these, anon. tattle happens more often than public tattle.

I suggest a bag of tokens. (Note that a deck of cards is mechanically similar to a bag of tokens, but tokens are easier to "shuffle" and provide a greater level of anonymity.)

The Bag:
The bag of tokens metaphysically represents the authority figure that you're tattling to. It starts pre-populated with a number of "no action" tokens. (Note that these "no action" tokens could include minor game effects. The relevant thing is that these tokens do not act as tattling tokens.) The more "no action" tokens the bag starts with, the less likely the authority figure is to act on tattler tips; adjusting this will significantly change how the game plays.

The Tokens:
You (and each other player) start with piles of anon. tattler tokens (one pile to tattle on each other player), piles of public tattler tokens that identify you as the tattler (again, one pile to tattle on each other player), and a screen to hide your token piles from the other players.

Tattling:
At various times during play (When? That's up to you. I don't know enough about the game you're creating to really offer a good solution here.), the Authority bag gets passed around from player to player. When you get the bag, you MUST put your hand in the bag, jostle the tokens that are in the bag, then pass the bag to the next player. The important thing here is that you must make it look like you added a token to the Authority bag, whether you did or did not.

Game pressures encourage the players to prefer their anon. tattler tokens over their public tattler tokens, making anonymous tattling more likely. As you run out of anon. tattler tokens, you'll have to use your public tattler tokens and you'll be exposed for the rat you are! Alternately, you can make a rule that says that when you add tokens, you add two anon. tattler tokens and one public tattler token. However, this requires complete honesty and could fail due to accidental or intentional cheating. It's easier to just give players more anon. tattler tokens than public tattler tokens (perhaps a 2:1 ratio?). Also, this gives players a strategic element to consider: Tattler publicly early, then anon. tattle later, or vice versa?

Another way this can work: All players start with a small number of both types of tattle tokens. During play, you may do things that are "illegal". When you do, each other player gets more public and anon. tattle tokens to use against you. These tokens come from a public pool and go to each other player's private (hidden) pool.

Consequences:
At various times during play, one or more tokens get drawn from the Authority bag. "No Action" tokens do nothing. Anon. Tattler tokens punish the player the token identifies. Public Tattler tokens punish the player that the token identifies, but everyone knows who tattled.

Mechanically, the authority becomes more likely to go after a player than do nothing as the ratio of tokens shifts from "no action" to tattle tokens. If this isn't what you want, you can add a stash of "no action" tokens to each player's secret stash. When you get the Authority bag, you can add no tokens, or any one token you want to add.

Etc.:
Whew! That's where I'm at with this. Those are my thoughts.

(Goes and reads the rest of the thread.)

Okay. My ideas don't seem too different from the others presented on the surface, but the token bag does bring several significant mechanical differences. Notably, that ratting is persistent - a prior ratting maintains its presence from turn to turn. If this is an issue, there needs to be a way to flush the tokens from the Authority bag from round to round without anyone seeing what was in the bag. You could do this by prepping multiple bags at the start of the game (Play rounds 1-3 with the red bag, 4-6 with the yellow bag, and 7-9 with the blue bag), or by periodically dumping the contents into the box (without looking at what comes out) and resetting the bag.

The action taken by a player when he wishes to rat must be taken by all players at the same time, or just simply taking the action would declare him as the originator of the accusation. (be it drawing a card or placing a chit in a bag or anything.

on top of that, it seems you have two bits of information that you want to be revealed at different times, the target and the originator. Those two bits of info should be kept separate, (i.e. 2 cards or two different chits)

Also you may at times have multiple originators who wish to rat at the same time, so their two cards or chits must be kept separate from another players who wish to rat at the same time.

so my thought is when the ratting time comes, have everyone place two cards on the table randomly (have everyone look away or something.) Each player may place cards designating the target of their rat and then an identifier card designating them as the ratter. Then design a random way to reveal these two cards separately, based on a die roll or something else.

Alternatively a player who did not wish to rat could place 2 decoy cards with no information.

Anyway just break your problem down to its base elements and solve your problem there.

Have Fun!

Instead of forcing all players to rat at the same time (although you still can do this), make ratting a part of each player's turn (like drawing a full hand of cards would be). At the start of the turn, you grab the bag, put your hand in, and shake it up. You may or may not be adding a token to the bag when you do this.

Alternately: If you really, really want players to be able to rat any time they want to, make the action of taking the bag, putting your hand in, and taking it out again an essential part of getting a useful in-game advantage. Example: "You may [process of ratting] at the beginning of any other player's turn to discard your hand and draw three cards." You look like you're ratting, but when someone calls you on it you say, "I needed better cards. If you had the cards I had, you'd've done it too."

1) It might be stuck in your hand and you want to get rid of it. Also, playing it and getting away with it might give you points.
2) Yes. That's why you'd need quite a lot of anonymous non-rat cards.

OK, the hardest case is the following: -

1) Players can rat on anyone at any time
2) If someone rats on someone else then it should have a game effect more or less immediately
3) If someone rats on someone else, then it should be usually be hard for any other players to determine who the rat was

Clearly, 1) 2) and 3) together mean that whenever someone rats, everyone else has to behave in an outwardly identical fashion. This suggests that you can't voluntarily initiate an anonymous ratting, since your anonymity will be compromised by the fact you initiated the rat-a-round. I'd guess that the cleanest way to solve this is to force everyone to rat-or-not-rat at predefined times (e.g. each turn or each round).

It's not obvious that it can be done without custom components; here's another try:

Components (players are identified by colours or icons):
2 decks of cards with readily distinguished backs, which I'll call "Rat" and "Trace" decks.
The Rat deck consists of some player-identified cards and a lot of blank "Nobody" cards.
The Trace deck consists of some player-identified cards and a lot of blank "Anonymous" cards.

Setup:
Each player gets an individual Trace deck consisting of all their own Trace cards and a number of Anonymous blanks shuffled together.
Each player may also get a few of each Rat card for convenience.

Mechanic:
In the rat-a-round, each player chooses a Rat card and plays it without anyone else seeing what it is. To rat on player X, choose and play a "Rat X Out" card. To abstain from ratting, choose and play a "Rat Nobody Out" card. Then, without looking at it, the player deals a card from their Trace deck face down on top of their Rat card. Most of these Trace cards will be blank, but some will identify the player.

Somehow, randomise these card pairs (e.g. everyone turns away while player A mixes them up, then everyone turns away while player B mixes them up). Then, reveal N pairs (N will determine how likely ratting is to have an immediate effect).

Properties:
* Each rat-a-round, each player may rat out one person or nobody
* There is a small and easily design-tunable probability that your action (rat or don't rat) can be traced back to you
* You cannot know in advance whether your action is traceable
* Requires randomising pairs of cards (or other components) while keeping the pairings intact

Variant:
* The Trace decks can contain ambiguous cards as well, e.g. cards with pairs of colours on them, which go in more than one player's Trace deck.

I did not read completely your post, but I think I have an idea that could help you.

I want to implement an espionage system in one of my game. For all the examples below, you need a series of cards that contains the special event/effect and a target player color.

Then you can have many options. each player draw X cards and play y card. Shuffle and reveal all or some of the cards played. You can also add cards randomly to the deck of played cards so that the players does not know if there is really somebody targetting them.

Another variant, select x cards randomly from the top of the deck and give y cards to everyplayer. Then draft this deck of cards from a player to another. Each player can remove y cards and add z cards to the deck.

This mechanic is more interesting because you can do counter espionage (discard a card targetting you) and you can try to guess who is plotting against you. (I did not had any cards targetting me but when it reached the end of the table I got 3 bad events, so these players are plotting against me).

In summary, the espionage system is linked with the random event system and the players can influence it's outcome.

Since you need to make each special effect for each player color, this system would work great if you do not have that many special effects.

Everyone puts in a card in turn order (RAT OR NO RAT) top to bottom.

Before, anything is done, a second randomized stack of conditions are shuffled and the top card is revealed.

Choices of this second stack should be a mix of the following cards in whatever percentage you desire:

Reveal the first player's card.
Reveal the second player's card.
Reveal the third player's card.
Reveal the fourth player's card.
Do nothing.
Randomize and reveal a card.

Setup for 1 Cop Player and 3/5 Criminal Players. Criminals have each one hitman per player in the game, six tokens with their respective colour, 4 bribes tokens and a 48 cards deck for all of them, Cop has two detectives per player in the game. Game board depicts 6 treasure locations to steal from and a Jail. Plus, a central Rat cards pile space, six Action card pile spaces, one for each Criminal player.

Objective: the Criminal players have to steal treasure locations and the Cop has to nail hitmans and collect bribes. Game ends with a Criminal stealing all treasures or a Cop having less than two detectives.

Scoring: Criminals get 1 Victory Point for their first hit, 2 for the second, 3 for the third, and so on. Cop gets 1 VP per hitman caught and 1 VP per bribe collected.

Setup: All players start with 10 cards minus the number of players, all their hitmen and detectives.

Turn sequence: at their turn the Criminals can play one card facing down in the Rat pile and one card facing down in their own Action pile. Then the Cop reveals the Rat cards and decides to deploy detectives into "ratted" locations and/or take an offered bribe to stay away of a "ratted" location. Then all Criminal's Action cards are revealed and effects are resolved. At the end of the turn, all players replace the number of cards played (one or two). Criminals that steal a treasure location place a token of their colour there. If the Cop deployed a detective where their were planning a robbery, their hitman is caught and placed in the Jail. If their hitman was deployed in a "Hit" assignment, a detective arriving there will be killed. Hitmans can be released from Jail by paying 2 bribe tokens. Extra bribe tokens (4) can be gained by returning a treasure solen (remove token from treasure location).

Criminals cards deck: Steal treasure location 1 to 6 (2 x 6 different cards), Rat a posible Hit in treasure location 1 to 6 (2 x 6 different cards), Set a Hitman in location 1 to 6 (2 x 6 different cards), Offer bribe to clear treasure location 1 to 6 (1 x 6 different cards).

PS I'm with the previous posts here, if the game is "Ratting" and is not an abstract, you shoud stick to a mafia or espionaje theme.

Keep thinking!