The best replacement for sourcetree is tower.

The best alternatives to sourcetree are rated as following:
★★★★★  tower
★★★★★  github
★★★★  tortoisehg
★★★  github for mac
★★★  smartgit
★★★  machg
★★  github for windows
★★  gitx
★★  github app
★  stash
★  git gui
★  giteye
★  gitbox
  git extensions

Your alternative for sourcetree is not listed? Suggest!
Speaking about sourcetree, one probably shouldn't forget about github.

Other search terms related to sourcetree and their ratings are:
★★★★★ github
★ gitlab
You have in mind a companion for sourcetree and it is not yet here? Propose!



Google Trends

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sourcetree
tower
github