This is a slackin clone written in Go because... Node.js bloat and Go is much nicer :-)
Install or update with
go get -u github.com/flexd/slackinviter. Run
-h for help, it just takes recaptcha secret + sitekey + slack api token as parameter, and listenAddr.
See https://cognitive.io/post/rewriting-the-gophers-invite-form-in-go/ to understand why I decided to rewrite Slackin in Go.
Visit https://invite.slack.golangbridge.org to see the real thing, or look at this
SLACKINVITER_DEBUG=1to turn on debug logs for the slack api