Endless Sky is a GPL-licensed space exploration and combat game with a narrative bent, akin to EV: Nova (an old shareware game for Mac, Linux, and Windows), though gameplay will also seem familiar to players of Transcendence or Stellar Frontier.
One of the things that makes Endless Sky so engaging is its focus on strong storytelling and narrative play; it takes place in a massive galaxy full of solar systems to explore and fight in. There are a number of factions, one of which currently has a full storyline available. Factions remember what the player does, so they have to be careful and watch their step if they want to be able to travel freely through certain parts of the galaxy.
Of course, another strength of Endless Sky, inherited from its spiritual predecessor EV: Nova is the ability to be extended and expanded in various ways. I have created a couple “plugins” for Endless Sky, some of which are primarily of interest for debugging and testing, while others are focused on expanding gameplay and ship customization for the average player.
Cannon Friendly (pun intended) is my personal gameplay enhancer for Endless Sky; it comes with new weapons (currently limited to just the autocannon and autocannon turret, which mimics a classic EV: Nova weapon) and outfits available at various places throughout the galaxy, each of which will eventually have all the art assets and variant integration required to be near-indistinguishable from the original game’s content.
Cannon Friendly Weapon Pack 0.3 (Sept 5 2015) Cannon Friendly Weapon Pack (without image sources) 0.3
The Ship Improvement Cheat and Expanded Maps plugin permits players to easily buff up their ship (with a cheat improvement that makes the user’s ship gain massively more available space and improved attributes), or buy maps that expand the edges of the known universe.