This looks promising! I help run local meetups for systems programmers [0] in cities across the world. We've been looking for a self-hosted RSVP system for ages (and haven't had the time to build one.)
We'll take Cactoide out for a spin for our September meetups! I'll open up some GitHub issues if any blockers show up.
Coool! If you have any trouble with the spinup just contact me.