Nurx at-home HPV screening kit - Assess your risk for cervical cancer at home
Documize - Enterprise-grade wiki and knowledge management platform
Server Fault - Server Fault is a Q&A site for system administrators and IT professionals that's free.
HackMD - Fast and flexible, real-time collaborative markdown, inspired by Hackpad.
Dadi - Store your sperm. Stop the clock.
ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.