Hamsterpad - Slack is an awesome chat system, but getting traction for your own Slack group or finding other interesting Slack groups can be a little tricky. Hamsterpad is an index of Slack groups.
Maitre - Give early access to people based on their spot in the waiting queue, but move them up in the queue if they get people to sign up via a special link. This is a super effective viral growth tool.
Slaask - Handsome support chat (it looks like Intercom) that interfaces with Slack? And it’s free??? I plan to use this for my own projects. I’m amazed it didn’t get more attention on Product Hunt.
Patreon - Interesting payment platform. If you have a podcast (or another creative endeavor) people can automatically give you $5 or something a month to help support your efforts. Some people are raising $100k+ a year for their podcasts this way. It beats giving money to public radio, right? (Oh and if you want to get funds this way, sign up via that special link and you can get a bonus based on how many supporters you get in the first 30 days, between $50 and $500 extra)