The best replacement for assembla is unfuddle.

The best alternatives to assembla are rated as following:
★★★★★  unfuddle
★★★  github
★★★  jira
★★★  bitbucket
★★  codespaces
★★  pivotal tracker
★★  beanstalk
★★  basecamp
★★  cloudforge
★  atlassian
★  projectlocker
★  google code
  codesion
  rally

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

Other search terms related to assembla and their ratings are:
★★★★★ ankhsvn
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