The best replacement for playon is tversity.

The best alternatives to playon are rated as following:
★★★★★  tversity
★★★  plex
★★  hulu plus
★  hulu
★  xbmc
★  boxee
★  orb
★  ps3 media server
★  playlater
★  serviio
  aereo
  twonky

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Speaking about playon, one probably shouldn't forget about free roku.

Other search terms related to playon and their ratings are:
★★★★★ free roku
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playon
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