Architects

The "Architects", or hyperspace aliens, is the name given to a mysterious race that at some time in the distant past, visited the Galaxy and interfered with its geography and cultures.

Nothing is known about their origin, whether they were endogalactic, or extragalactic (like the Yuuzhan Vong) and what happened to them.

To them are attributed some unexplained things in the Galaxy, like the building of Centerpoint Station and the artificial position of the planets of Corellian system (although the best candidates are the Rakata, the Killiks and the Celestials [note: the articles Centerpoint Station and Celestials are contradicting]), the appearance of human-like species in various systems etc.

These aliens could be, or be related to the Celestials, the Killiks or the Rakata, who claim to be the inventors of the hyperdrive. The Rakata were the ones who taught the Corellians the secret of hyperdrive technology, a feat previously attributed to the Architects.

Behind the scenes
"Hyperspace aliens" is a fanon nickname of the otherwise undescribed aliens who according to Star Wars: The Roleplaying Game, gave the hyperspace technology to humans.

According to The New Essential Chronology, the Rakata were the originators of the technology, from where the Corellians adopted it, giving therefore a possible solution to the "mystery", though the book refers to the Architects, the famed hyperspace aliens separately from the Rakata.