Thanks for asking!
Sojourn hasn’t been distributed under a license yet, though it likely will be in the future. I firmly believe that game rules and mechanics are not intellectual property. Folks are free to take rules or mechanics from Sojourn and use or remix them in any way they please (though a shout-out is always appreciated).
If another game designer wants to borrow direct text from Sojourn, I would just ask that they quote and cite as they would any other book. Anyone is welcome to advertise their games as “Sojourn Compatible” so long as they do not indicate the game is published or endorsed by me or Sojourn RPG Publishing.
As for sharing, I encourage players who need extra Sojourn copies but can’t afford them to download free Community Copies from here on itch.io. It’s helpful to be able to keep track of download numbers this way, so I do appreciate it when people grab whatever extra PDFs they need here instead of elsewhere.
A hyperlinked version of the level 1 starter rules is also freely available at sojournrpg.net. The advanced rules and full spell list will eventually be added there as well.