Stack Overflow Documentation - A crowdsourced developer documentation
Writty - An open-source text editor to help you focus on what matters
Archbee.io - Archbee is a developer-focused product docs tool for your team. Build beautiful product documentation sites or internal wikis/knowledge bases to get your team and product knowledge in one place.
Everypixel - Stock Image Search Engine That Filters Out Trash. Made for designers who hate bad stock images.
Slite - Your company knowledge
Paircast - Document code by aligning screencasts with code changes