Subversion is open source version control software.
Not in the Top 100 in 2013
Comments from some of those who selected Subversion as one of their Top Tools
“Most people who are not using a file version management system should! Subversion is one of the best around!” Daniel Lemire
“A database for documents and files with version control. Gives the team central place for saving and keeping documents. We have used a variety of version control systems, but Subversion is pretty easy to use” Ulrik Juul Christensen