Slackin
Public Slack organizations made easy
...It provides a landing page where visitors can enter an email address and request an invitation to a configured workspace. The service can also expose badges showing the number of connected users. A realtime badge uses Socket.IO, while an SVG version works in static pages such as README files. Google reCAPTCHA support helps reduce automated abuse of public invitation forms. Slackin can run as a standalone HTTP server or be embedded into another Node.js application through its Express-based API. The project reflects an older generation of Slack invitation workflows and may require adaptation for current Slack platform policies and APIs.