The best replacement for tfs is subversion.

The best alternatives to tfs are rated as following:
★★★★★  subversion
★★★★  git
★★★★  svn
★★★★  jira
★★★★  vss
★★  github
★★  afr
★★  rally
★★  jenkins
★  sourcesafe
★  visual studio online
★  version one
★  hp alm
★  rtc
★  tfs express
★  mks
★  clearquest
★  clearcase
  ontime
  mercurial
  perforce
  accurev
  project server
  cobra intake
  qc

Your alternative for tfs is not listed? Suggest!
Speaking about tfs, one probably shouldn't forget about visual studio.

Other search terms related to tfs and their ratings are:
★★★★★ visual studio
★★★★★ sharepoint
★★★★★ git
★★★★ visual studio 2008
★★★★ jenkins
★★★★ visual studio 2012
★★★ mercurial
★★★ xcode
★★ project server
★★ visual studio 2010 express
★ vs 2008
★ sharepoint 2010
sharepoint 2010 integration
ssms
You have in mind a companion for tfs and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of tfs in all years. Click on graph for more.
tfs
subversion
git