For a long time, the choices were between SCCS (if you were running a commercial Unix), RCS, and CVS. There is now a lively set of work ongoing in this regard: Wikipedia:Category:Free_revision_control_software.
Unlike CVS and Subversion, which are SCMs that have a single central repository to which others may subscribe, and similarly to some other SCMs such as Monotone, Darcs, and Arch, Git is a "distributed" system. That is, supports the notion that each user has a copy of the repository, and rather than one being an authority, each node is (in principle) a "master" node, and changes can be copied from repository to repository.
The design model for Git is that it tries to look something like a distributed, versioned filesystem; further tools (CoGito and StGit) have built CVS-like command interfaces on top of it.
Meetings:2007-08 involved a talk about Git by Pavel Zaitsev.