Distant Stars is a huge enhancement mod that increases the visual appeal and gameplay of Sins of a Solar Empire. DS, as it's referred to in the shorthand, allows you to research more upgrades, build more ships, has more variation to the strike craft and planet defenses, and settle more planet types. It also improves the pirate faction to make them a threat worth dealing with, as well as making it tougher to take over their home asteroid.
Being that this mod enhances most of the visuals and sounds, it's recommended that you turn your settings down from highest to at most high or lower on older systems to avoid hitting the 2 Gig RAM usage limit too quickly. There is also a multiplayer add on patch that incorporates some of the Sins Optimization Project and other quick fixes to help improve the multiplayer speeds.
For more information on the mod, download locations, lore, and much more, please visit the DS Mod Wikia page.
Notice: Like most mods, DS is in a Beta stage and is continually being developed for all three versions of Sins. Bugs are generally fixed in the version released after it's discovered, and support is usually quickly offered by the team and other members of the community via the SoaSE forums.