This is a bit of an odd one, Adventure Land is an MMO where you code characters using either the provided code or do a little of your own to help you progress. They plan to go open source too.
Adventure Land sounds like quite a sandbox MMO, one with no specific quest-line to follow, no guides you have to follow and so on. They say you can "trade, gamble in tavern, party with friends, pvp solo with your rogue or go after rare loot".
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As for going open source, their Steam page claims "open-source at 50,000 installs" so that should be quite interesting to see if they ever do it.
They seem to need a bit of help with testing the Linux version, as their news post states:
Published the Mac and Linux versions of the game on Sunday, Linux version was heavily requested, sadly the Linux version ended up being very problematic, Linux users are natural problem solvers so things seem to work out, but I do wish things worked out of the box, last issue I worked on was GPU related, can't assess whether it was an isolated issue or whether it will be widespread, if you are reading this and using Linux, looking for feedback