As already stated, it was the Coalition, during the Sol War, that developped something that ressembles the actual jumpgates. The only differences are that they were only able to travel distance from a planet to another (Imagine, in big, taking a Jumpgate from Manhattan to Pittsburgh) and that they were VERY unstable. When the 45th Squadron of Volunteers discovered one, along with another German squad, they were catapulted from Jupiter to Venus, and was directly into the enemy's line, inside a fortified outpost.
As the 45th of Volunteers had no Bomber backup to destroy the stations, and were heavily outnumbered, they decided destroyed the gate's engines and when they succeeded, a strong gravity field engaged, taking back most fighters into the gate. Rumors are that when the gate exploded, the blast it created was so fierce that nothing was left of the Coalition fortified station.
As answer to this new threat, (The Coalition could easily assemble a fleet by Venus and send them all to Pluto without being detected.), the Alliance created a new technology themselves: Portable Wormholes, installed mostly on stealthy fighters, but some capital ships were known to have some, such as the ANS Yamato, that could carry them around the Sol system just like the Coalition's gate. The only drawback is that it takes quite some time to recharge.
The 45th of Volunteers, considered as the best squadron the Alliance had, were often asked to use ships that were able to turn invisible, just like Rheinland's invisibility system, and to raid capital Coalition stations, mostly for their fuels, ammo and weapons.
In big, Stealth technology and Jumpgates already existed in Starlancer, and were all developped because of the Sol System War.