The launch date hasn't been revealed yet by the developer
Gratuitous Space Battles, a title developed by the Positech Games studios, will be available on Steam for Linux, soon.Gratuitous Space Battles has been available for a few years and it was already ported for Linux for a Humble Bundle. According to the CDR database, Gratuitous Space Battles is set to be released on the Linux platform in the near future.
The game is a combination between the real-time strategy and the tower-defense genres. The players will only be responsible for building and placing units, but they will not be able to interfere with the actually battle. All order will be given before the engagement and you get to watch, relax and enjoy the fireworks.
The other part of this information is taken from the CDR database and by no means is it completely certain. The CDR Database is a record of data that describes every Steam game and subscription provided by Valve for the Steam service.
Usually, the new entries in the Steam database are first visible in the CDR Database before their official launch.
If you are interested in this game, you should check out the official Steam website.