One can make money from DCRW: Dungeon Crawl Race War. It will feature built-in cryptocurrency betting, for either PvE or PvP. While the code is open source, the bookies take a cut.
PvP just means both players agree to a set of conditions and an objective, then they both do a run on the same server, and the server enforces the rules and declares a winner.
So the money is running a book, running a server, betting intelligently, and presumably also in being an elite player, since there will likely be prizes to encourage betting.
There's also incentive to pay for code that will increase revenue.
I imagine from there other revenue streams are possible, as other OSS businesses have done.
I'm still working on the DCRW project, still writing rough drafts, pre notes consolidation. I blog at / and https://saidit.net/s/dcss/