Documize - Enterprise-grade wiki and knowledge management platform
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
Boardist - Personal workspace for all the data
Standard Notes - A safe place for your notes, thoughts, and life's work
ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.