Multiple commercial versions of the game were released in addition to the free ports. Apple Inc. released a version for the Apple II+ called "Apple Trek" in 1979, and Atari, Inc. released a version for the Atari 2600 as "Stellar Track" in 1980. The TRS-80 had at least three separate commercially available Star Trek games, including "Trek-80" by Processor Technology (later retitled "Invasion Force") which added more interactivity and a number of new options incorporated from the unrelated "Trek73", a second "Trek-80" by Judges Guild, and "Startrek 3.5" from Adventure International. Acornsoft released a version titled "Galaxy" for their computer systems, and Tandy Computers released "Space Trek" for theirs. Yet another version was written in BASICA for the IBM Personal Computer in 1982, "Video Trek 88"; written by Windmill Software, it used numbers for most commands, like the earlier "BYTE" version. Apex Software released "TI-Trek" for the Texas Instruments TI-99/4A in 1983, which incorporates speech if the speech synthesizer is present. 1984's "" by Interstel was a variant released commercially for several computer systems. This game was successful enough to spawn a series.