"Colony Wars" Series
"Colony Wars" consists of three games exclusive to the PS1, letting players pilot various spaceships in missions against different factions in the style of the "TIE Fighter" series. "Colony Wars" is best remembered for its branching storylines, which change depending on failure or success of various missions. Each game has at least five different endings.
"Homeworld" Series
Relic developed "Homeworld" and "Homeworld 2," released in 1999 and 2003 respectively. Both games are about a fleet of ships trying to cross hostile space in order to return to the safety of their home planet system. The "Homeworld" series is unique among real-time strategy (RTS) games in the sense that resources and units are scarce and the skirmishes are about minimizing damage and loss, as you play the same fleet of ships throughout the entire campaign.
"Descent: Freespace" Series
"Freespace" and "Freespace 2" were developed by Volition, released in 1998 and 1999 respectively. The focus of these games is piloting various fighter-sized starships in dogfights with enemy forces. The novelty of the environment focuses on freeform movement, taking some cues from Newtonian physics to simulate frictionless, weightless "free space," as opposed to tradition space flight sims which don't attempt to account for the unique physical properties of space travel. In addition to this, players can also command huge capital ships to lay siege to the opponent's large ships with beam and missile weapons.
"X" Series
The "X" series is a PC-exclusive strategy simulation series of staggering scale, encompassing everything from diplomacy, research, warfare, trading, industry and economy. Players of this game command many fleets, outposts and colonies and frequently come into conflict with A.I. opponents over disputed or uncharted space. The fully customizable ship loadouts, governing top speed, acceleration, weapons platforms and defense, lead to very complex and daunting battles, with hundreds of fighters, frigates and capital ships.