Is there an existing mod...?
 

I'm an administrator of a forum which is used to arrange regular face-to-face gatherings that are open to attendance by any members. Currently, if members are planing on attending, they copy the list so far and paste it with their username added to the bottom. It works for the most part, but is very messy. I'm hoping there is a mod out there somewhere that would add a users name to the list by them clicking a button attached to the first post in the thread. I've searched these forums but am not really sure what keywords to use to describe the features I'm looking for. The nearest mod I can find is the 'Thanks' mod.

Ideally, I'd like to have the option of customising the button/ adding more than one (one to say 'Possible', another to say 'Definite'). And also have the ability for members to remove their name from the list if necessary.

Does such a beast exist (either in full or part)?