The best replacement for lightroom is aperture.

The best alternatives to lightroom are rated as following:
★★★★★  aperture
★★★★★  photoshop
★★★★  bridge
★★★  elements
★★  iphoto
★★  picasa
★  camera raw
★  photoshop elements
★  capture one
★  aperture 2
★  aperture 3
★  gimp
★  dxo
★  cs3
  elements 12
  capture nx
  capture nx2
  photoshop cs6
  photoshop elements 12
  cs6
  cs5
  aperture mac
  acr
  darktable
  dpp
  cs
  photoshop for raw
  acdsee
  lightzone
  aperture 2013
  bibble
  paint shop pro
  photoshop cs5
  adobe photoshop
  nx2
  adobe camera raw
  photoshop cc
  apple aperture
  bridge cs5
  elements 11
  elements 9
  cs4
  adobe bridge
  pixelmator
  aperture 2.0
  photoshop elements 10
  pse

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

Other search terms related to lightroom and their ratings are:
★★★★★ photoshop
★★★★ vsco
★★★★ gimp
★★★ wacom
★★★ iphoto library
★★ wacom tablet
★★ cs3
★★ photoshop elements
★ jpegs
You have in mind a companion for lightroom and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of lightroom in all years. Click on graph for more.
lightroom
aperture
photoshop