SpaceSimCentral

Ad-Infinitum
Space game of galactic conquest. Real time/turn based strategy with civilization type colonization of worlds. Influences include: Civ, Master of Orion, emperor of the Fading Suns, Dune. Universe a future dark age with noble houses vying for control.
Download: http://sourceforge.net/projects/ad-infinitum/files/
Status: Under Development

Dominium
Dominium is a space combat/trading/explorer game for PC, Mac, Linux and iOS. Fly and fight your way across a galaxy as a lone pilot or wingman, or buy and run a fleet of ships with others doing your bidding, or buy Space Stations and run an entire economy!
Homepage: Dominium Homepage
Status: Under Development

FAR Colony
FAR Colony (First Autonomous Remote Colony) is a game of exploration and space colonization being held in the 23th century. It has 2 phases: a Colonization Phase where the player must establish a new colony on a pre-determined planet and has 365 standard days to make the colony viable. In the second one, the game is purely sandbox, and the player can develop his/her colony as he/she likes. AI and game/historical events will set many goals and problems to manage.
Homepage: FAR Colony Website

FFED3D
FFED3D is a remake of Frontier First Encounters that adds D3D and more. Talk about playability, configuration, and modding.

Oolite
Oolite is a space sim game, inspired by Elite, powered by Objective-C and OpenGL, and designed as a small game that is easy for users to pick up, modify and expand upon. Almost every aspect of the game can be changed by using simple, free graphics packages and text editors.
Website: Oolite Homepage
Forums: https://bb.oolite.space
Gallery: Oolite Gallery
Downloads: Oolite Downloads

XFrontier
XFrontier is yet another Frontier-Elite 2 remake, with some key features that should differentiate it from the original project : planets with improved rendering, virtual cockpits, game contents and rules totally moddable through lua-scripting, option of leaving your pilot's seat and explore your ship and the surface of planets by yourself.
Homepage: http://bidouillefrenetique.blogspot.fr/