This is something I have worked on as a tool for those of you who want to run a game, but don't feel like learning and adapting an existing system or creating one of your own. You can use it if you want, but you don't have to. Feel free to create your own.
The Pareidolia System.
The game will begin when the Storyteller posts an introduction of the setting and the predicament that the characters find themselves (whatever that may be). All the players will then post introduction scenes for their characters. All players will then post their actions and dialogues and such until the Storyteller posts an event scene(s). The players will then post reaction scenes. Finally, the Storyteller will post the resolution scene(s). The game will go on like this (role-play, event, reaction, resolution, role-play) until it reaches some sort of ending, of course. The game will end with a conclusion scene by the Storyteller. In addition to these posts, the Storyteller will also send the players private messages that will play into the game, labeled "Personal variations" and "Text messages."
Introduction scenes. The players will basically describe who their characters are and what their reactions are to the opening predicament. You can put as much or as little information into these as you want. I only advise against putting too much detail of your character into these since you may want to reveal something later on or even just to cut down on the potential for metagaming, but this advice isn't a rule.
Event scenes. The Storyteller will describe something that happens to or around the characters. If all of the characters aren't in the same area (as in, they all happen to be in different places around the setting), the event scene can be split up accordingly to handle this. Maybe different events are happening to different characters since they're in different locations. Storytellers can use their own discretion in handling this kind of situation.
Reaction scenes. The players will describe how their characters react to the event scene(s). Pretty self-explanatory, I'd hope. If not, then feel free to ask.
Resolution scenes. The Storyteller will describe what happens to the "event" based on the characters' actions. Since this is a diceless resolution system, Storytellers will have to make their own judgements as to what happens. Try to be fair but firm. Reward good and clever actions; punish bad and stupid actions. You don't necessarily have to kill the character for doing something stupid, but don't let them off easy either. As this will probably be used for horror / creepy games, terrible consequences for bad decisions are very likely. A resolution can lead into another event scene, so repeat as needed until the whole thing is resolved somehow (victory or defeat).
Conclusion scenes. The Storyteller will describe the ending of the game. Whether that means everybody died or somebody suceeded in accomplishing some goal, this will be how the game ends. Maybe it's an epilogue, showing what happened to any characters that might have survived in some fashion. Or maybe it's just a simple "And then they all died. How sad." It, of course, depends on the game and what happens.
Personal variations. The Storyteller will describe (in private message) something that may be different about the setting, predicament, or events for the character whose player receives this message. For example: Say a monster with reddish fur attacks the whole group, but in the personal variation, the monster looks like it has blue-ish fur to one of the characters. While an extremely simplistic example, it still illustrates my point. Players can have their characters react to these variations however they'd like, but they cannot be ignored completely.
Text messages. The Storyteller will send the player a message for their character. Not all games or characters must have a cellphone just to utilize this option in your game (no communication can add to the atmosphere!), but games and characters that do have them, it opens up a lot of room for stuff. Especially in games that rely on mind screwy kind of material. This can also be used for players to have their characters communicate amongst themselves by talking through text messages (in this case, the players would just private message each other using "text message" in the subject; unless the Storyteller wants to monitor the conversation to use stuff from it for the game, then the players would have to message the Storyteller and they would send the message to the other player). Phone calls are out of the question, however.
Diceless system. As there is currently no way to roll dice on the forum and I know I wouldn't trust a dice roll I can't see (plus, I really hate using dice in role-playing anyway; luck-based stuff just sucks), this system will be diceless. Resolutions will be at the discretion of the Storytellers. Also, that means there won't be any stats and such to keep track of. Use what is humanly possible based on your description of your character and try to be as realistic as you possibly can be. Games that include supernatural abilities for the characters should be handled with extreme care.
Don't say "No." This is an option for Storytellers to use; they can choice not to use it if they'd like, though. It is something I "borrowed" from another game (Nobilis). It basically boils down to not outright saying "No" to an action a player may want their character to make (with some exception). You can say stuff like "Yes" (obviously), "How?" (for when a character does something that the player needs to justify how the character would do it), "You can try" (for actions that seem weird or just plain dumb), and "Maybe, but there's a catch" (for actions that can be done, but not without a consequence of some kind). Naturally, players should try not to go above and beyond what their character should be realistically capable of and the Storyteller can still say "No" to certain actions (like a character trying to lift something heavier than they should be able to lift without a damn good justification from the player), but this is a way to not completely discourage a player from trying to act creatively.
Anything else? Nothing at the moment. This should pretty much cover everything necessary for a game. If I think of anything else or you all think of something I may have missed, I will adjust the system. If a situation comes up that isn't covered by the system, the Storyteller should feel free to handle the situation in a decent manner and then we will adjust the system for that kind of thing for next time.