According to Wikipedia space sims which offer trade and basic diplomacy are not 4X titles. That being said it would be awesome if they made a 4X game using a solid spacesim engine. Anyway space sims I'd played include (and my rating for each as they stand now)
Wing Commander: Prophecy ― 6/10 (the best WC in my book, but pretty dated and clunky)
BANG! Gunship Elite ― 5/10 (ho hum)
Descent Freespace and Freespace 2 + SCP ― 9/10 (their reputation supercedes their actual influence)
Darklight Conflict ― 6/10 (a basic space shooter, lite on the sim part)
Freelancer ― 8/10 (a solid foundation that was never built upon)
Star Trek: Bridge Commander ― 7/10 (good tactical fun that gets samey fast)
Independence War 2: Edge of Chaos ― 6/10 (a solid sequel)
X2: The Threat ― 6/10 (basic 4X elements but weird and a patience-tester)
Space Interceptor: Project Freedom ― 6/10 (a passable budget game)
Lander ― 4/10 (just as the title implies)
StarLancer ― 7/10 (lame story, good combat)
Games I wish I'd played during their prime but reluctant to try now
Privateer II The Darkening
Frontier: Elite II
Hardwar
Star Wars: X-Wing Alliance
X-COM: Interceptor
Star Wars TIE Fighter: Collector's CD-ROM
Colony Wars
With the exception of continued community projects using the FS2 SCP engine/enhancements spacesims are a rarely-invoked legacy of the 20th century in a time where space exploration has become an expensive luxury. A shame too because spacesims offered thrills and spills that were almost unparalleled in 90s gaming.
