13th Moon is an atmospheric, story-driven space shooter, set 200 years in the future in unknown regions of space discovered by accidental wormholes in our own solar system. Interstellar travel still escapes humanity, but a new source of energy that could make it possible - a sort of natural super-battery is discovered in vast asteroid fields of this newly discovered space.
13th Moon plays like a vertical shmup, featuring levels in a chunk of space the player can explore mostly non-linearly (levels themselves are still played in a linear fashion).
The story and slight RPG elements are optional, and can be completely ignored by players that don't wish to engage with them.
The player's ship is completely modular with 50-ish different upgrades, many of which can be combined with others to change the way base weapons function.