Well this SEEMS like a semi straightforward idea. The party game Mafia is very popular around the internet, and it only seems fitting that minecraft have it's own incarnation. It would consist of: 1. A bot to run the system 2. A way of keeping track of everyone's roles 3. A voting system for lynches 4. Beds start night phase 5. Assorted powers that people can have during night phase (Mafia is TP'd to the hideout and get a private channel then are invisible so they can kill their victim, among others.) most of the plugin is already built into some other plugin's, but unifying them into one setup that only becomes active when admin issues some kind of /startmafia command would make it all very easy and seemless and most importantly fun.
Maybe I should have looked for this before I started making my plugin, but I had the same idea. I actually maintain an IRC mafia bot written in python. I just started learning Java today, but give me two or three weeks, and I should have a release ready.
This has been a little more difficult than I had planned. I can give you a temporary fix, I believe. Let me do a little work, and I can get you a modified IRC bot that might work with CraftIRC. It won't kill players, but it will be able to count votes, and if done right, set times. The bot is written in Python 3.2. EDIT: I have found a new direction, and if all goes well, I will be able to have this out before I head back to school.
Yours is outdated. Maybe mine will work for you. It is like this. http://dev.bukkit.org/bukkit-plugins/mafiacontinued/