Documize - Enterprise-grade wiki and knowledge management platform
Floobits - Floobits brings real-time collaborative editing to text editors, IDEs, and now Atom.
HackMD - Fast and flexible, real-time collaborative markdown, inspired by Hackpad.
codebunk - Realtime Collaborative Editor with Code Execution, REPLs and Chat
ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.
coderpad - Collaborative code editor with in-browser, real-time execution. Conduct programming phone screens like a boss.