riverrun's writeup above is an excellent
overview. I have just a few things to add.
Firstly, there essentially isn't any such thing as Avid Film Composer software anymore. All the 24fps editing capabilities of Film Composer were folded into Avid Media Composer by version 7 of Media Composer. MC software is now at version 10.x, but there was no version numbered 8.
Secondly, the Avid is no longer solely Macintosh-based. The Avid Symphony system, which is capable of handling uncompressed digital video (including High Definition video), runs on the Windows NT platform. Many Avid editors, myself included, saw this as a bit of a betrayal, but it is more likely the result of Avid's recent purchase of SoftImage (developers of high-end 3D animation and special effects software) from Microsoft than an indication of full-scale conversion to "PC" systems.
Avid Techology, Inc. develops and sells the following digital editing "solutions", among others:
Avid|DS
Avid|DS HD
Avid Symphony
Media Composer
Avid Xpress
Avid Xpress DV
SoftImage|XSI
Elastic Reality
Media Illusion
Marquee
Matador
Toonz
Avid also owns digidesign and, as such, develops ProTools.
For a somewhat clearer explanation of how the Avid solves the problem of the frame rate differential between film and video, please see 3:2 Pulldown.