Ruby on Rails

I'm still kinda new to Rails and was wondering if someone have ever been through this situation in any project. What I want to implement is a notification system, for a personal project I'm working into, something like a social network like Facebook that sends notifications to given users depending on some actions from one of the user.

Basically it's a "invite" notification where the receiver can accept/refuse and tell why did he refuse, so that the data may be corrected by the "event admin".

Any tips on where to get started? If anyone knows a good example code, or some Gem, or even general tips. Any help would be appreciated!

Thanks in advance,

Diego Dillenburg Bueno