The best replacement for activerecord is datamapper.

The best alternatives to activerecord are rated as following:
★★★★★  datamapper
★★★★★  orm
★★★★  sequel
★★★  sqlalchemy
★★★  mongoid
★★★  repository
★★  activemodel
★★  doctrine
★★  django orm
★  activeresource
  repository pattern
  data mapper

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

Other search terms related to activerecord and their ratings are:
★★★★★ rails
★★★★ sinatra
★★★ rails 3
★★ mongoid
arel
You have in mind a companion for activerecord and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of activerecord in all years. Click on graph for more.
activerecord
datamapper
orm