ProblemReporter for Sponge is a very easy to use plugin which adds a /problem command.
This command can be used to report a problem.
Players with permission are able to see what someone reported.
All the problems are being listed in the generated problemlist file.
(you can find it in the ProblemReporter directory in the mods folder)
Commands:
- problem
- problemlist*
- clearproblemlist*
*if the player is OP or has permission
Permissions:
- problemreporter.readhelplist
- problemreporter.clearhelplist
If you have any questions or problem, feel free to leave a reply 
Note: You can only download snapshots, this will change if Sponge is fully released.