Not to be pedantic but out of all of those, Outline is not actually open source; they're source available but they're using the BSL, which is "source available now and open source in the future"
Fair enough. BSL is technically not open source but it is endorsed by Bruce Perens of the Open Source Initiative and I believe it is a very good license for new startups in this space.
https://itsfoss.com/making-the-business-source-license-open-...