Quip - Quip is the modern productivity suite that simplifies your life and helps your team get work done faster.
Stonly Knowledge Base - Interactive knowledge bases and help-centers
Google Docs - Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.
Free Knowledge Base by Dashly - Optimize your customer support with Knowledge Base by Dashly
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.