While visiting Plexicorp in 1986, Montgomery Scott had the opportunity to use a Macintosh. Although initially baffled by the lack of a voice interface – he mistook the computer mouse for a microphone – Scott proved himself quite proficient in operating its "quaint" keyboard interface. (Star Trek IV: The Voyage Home)
Apple Computer Inc. – the official name of Apple in 1986 – is one of the few manufacturers to be the beneficiary of product placement in a Trek production. Kirk Thatcher suggested that the computer be a Macintosh. The production team originally wanted to use an Amiga for the scene, but that company was only willing to sell and not lend a computer for the film. Earlier versions of the story stated that there was a long wait list for the new Amiga 2000 computer and the Commodore employee fielding the request simply stated they'd have to wait in line to get one just like anyone else.
The production staff of the modern Star Trek series, including Denise Okuda, have frequently used Macintosh computers for both writing and artwork projects, including the Star Trek Encyclopedia and the Star Trek: The Next Generation Technical Manual.  On the sets of Star Trek: Enterprise, sixteen Power Mac G4 Cubes administrated by Michael Okuda were used to power the many computer display screens on the bridge, engineering, and sickbay sets, among others.  
- Apple Inc. at Wikipedia
- Macintosh at Wikipedia
- Macintosh Plus at Apple-History.com – stats and info page about the Macintosh Plus, the model seen in The Voyage Home
- Star Trek at the Apple Wiki – history of Star Trek at Apple Computer
- A Visit to the Enterprise Set at TrekNation – a guided tour of the Enterprise set, mentioning the behind-the-scenes computers and software setup