Some writer for
Star Trek: Voyager felt that the term
transwarp wasn't good enough so they renamed it Quantum Slipstream.
Quantum Slipstream is also the propulsion system used in
Andromeda. This is one of the more interesting takes on FTL travel that I have seen.
First off distance within the slipstream bears no relation with the distance in realspace, rather the distance is tied to the skill of the pilot and the regularity of passage by ships (regularly used routs are shorter than little used ones). This means that travel between two major worlds in different galaxies(For example, Tarn Vedra in Andromeda and Earth in the Milky Way) would be faster than a trip between two minor worlds that are in the same galaxy.
Another important point is that navigation MUST be done by a biological intelligence. The official explanation seems to indicate it is a combination of both pilots tending to make the correct choice, and the choice tending to make the path correct.
Like Star Trek's Warp Drive, Slipstream has the capacity for time travel under unusual circumstances (use of a purple pilot with unusual procognative abilities)