https://en.wikipedia.org/wiki/Spiral_Knights

Spiral Knights is a massively multiplayer online role-playing game created by Three Rings Design and published by Sega. The free-to-play, Java-based game was released in 2011, and continues to be updated.

In the game, the player controls a knight of the Spiral order, which has crash-landed on the mysterious planet Cradle. Knights cooperatively battle monsters throughout the Clockworks, the dungeon that fills the planet's interior. They also battle each other in an optional player-versus-player mode.

Additional links:

• Official website
• Wikia
• Steam
• TV Tropes