You have crashed.
You are stranded.
But you are not alone.
The Spiral Knights have awoken on an alien world. Their equipment stores have been raided and their starship, The Skylark, will not recover from the crash. Now they must work together to survive on a journey that will take them to the very core of the world.
It’s Java-based (between this and Minecraft, I’ve completely changed how I feel about Java games), and the site’s download page actually provides a Linux installer! There’s a wiki and a forum; the game itself is free, but an in-game “energy” mechanic limits your play to about an hour per day (you can choose to purchase more time). Here’s a bit more from the release announcement:
Finally, to all of our players I hope you enjoy the world that we have created for you. To me, it’s the best kind of world there is- a fun and mysterious place with equal parts fearsome monsters and good friends to have your back. But this world is special, it’s built to change. New adventures are coming, ones that require only the bravest of knights to band together and take the plunge.
See you in the Clockworks.