The best replacement for aperture is lightroom.

The best alternatives to aperture are rated as following:
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★★★★★  photoshop
★★★★  iphoto
★★★  photoshop elements
★★  shutter speed
★  lightroom 5
★  elements
★  picasa
★  f stop
★  iphoto 11
★  pixelmator
★  adobe lightroom
★  black mesa
★  lightroom 4
★  iso
★  depth of field
★  lightroom 3
★  iphoto library manager
  photoshop for mac
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  speed
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  photoshop cs6
  light pollution
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  small aperture
  photoshop cs3
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  cs5
  low aperture

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

Other search terms related to aperture and their ratings are:
★★★★★ photoshop elements
★★★★★ shutter speed
★★ depth of field
★ pixelmator
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Google Trends

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aperture
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photoshop