The best replacement for 5.5 is 6.0 project x.

The best alternatives to 5.5 are rated as following:
★★★★★  6.0 project x
★★  5.1
★★  s300
★★  6.0
★  7.5 redhawk
★  5.6
★  5.6 mysql
★  6.5 single six
★  exchange 2003
★  5.0
★  5 ipod
★  exchange 2000
  2.5 memory foam
  dg s300
  ipod 5
  dynamic gold s300
  nordic track 5.5

Your alternative for 5.5 is not listed? Suggest!
Speaking about 5.5, one probably shouldn't forget about esxi 5.1.

Other search terms related to 5.5 and their ratings are:
★★★★★ esxi 5.1
★★★ apache 2.2
★★★ vcenter 5.1
★★ apache 2.4
You have in mind a companion for 5.5 and it is not yet here? Propose!



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5.5
6.0 project x
5.1