A new patch is now automatically available for Syder Arcade on Steam, updating the indie action shmup (which is currently on sale for half off) to version 1.6. The update adds new content to the game, and also adds a new Linux version to go along with its Windows and OS X support. This page on the Steam community forums has the complete changelog for the new version. Here's word:

A new playable ship, The Overseer, joined the three already available: fast and deadly in combat, heavily relies on wraiths for damage and survivability and unleashes a powerful shockwave that destroys enemy bullets.

Two new challenge levels are now playable. The Lighthouse, where the gamer is called to defend the last bastion of Miza against a brutal pirate assault. The Ice Canyon, a race against time on the frozen moon of Ymir.

New Steam achievements have been added, together with a powerup born from a special collaboration. If you also own Unepic on Steam, some of the in-game pods will be transformed into cute, pixelated Baby Dragons from UnEpic. A similar surprise happens playing UnEpic with both games in the Steam library.