The best replacement for rails 3 is rails 2.

The best alternatives to rails 3 are rated as following:
★★★★★  rails 2
★★  rails 4
★★  4 performance
★★  mvc 3
★  sinatra
  merb

Your alternative for rails 3 is not listed? Suggest!
Speaking about rails 3, one probably shouldn't forget about mongodb.

Other search terms related to rails 3 and their ratings are:
★★★★★ mongodb
★★★★ datamapper
★★★ rspec
★★★ mongoid
★★ activerecord
★★ ruby 1.9
capistrano
You have in mind a companion for rails 3 and it is not yet here? Propose!



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rails 3
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