This article is from the storage FAQ part2, by Rodney D. Van Meter with numerous contributions by others.
This category of software can overlap with both HSM and backup, above, and basic tools are often available from the autochanger hardware vendors, below. New additions to this category welcome -- I'm sure there are numerous vendors I don't know. Functionality varies widely, from rudimentary "move the cartridge" interfaces to sophisticated tape-tracking databases. (rdv, 95/6/1)