Documize - Enterprise-grade wiki and knowledge management platform
Torchpad - Wiki farm with markdown based wikis.
HackMD - Fast and flexible, real-time collaborative markdown, inspired by Hackpad.
Referata - Referata offers hosting of semantic wikis, allowing you to add, structure and store data so it can...
ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.
ZuluPad - ZuluPad is a notepad on crack.