The best replacement for unison is rsync.

The best alternatives to unison are rated as following:
★★★★★  rsync
★★  harmony
★★  contemporary
★★  contemporary calphalon
★★  unite
★  gmb
★  btsync
★  freefilesync
★  sabnzbd
★  lsyncd
★  simply calphalon
★  calphalon contemporary
★  bittorrent sync
★  sennelier
★  rcn
★  csync2
  calphalon one
  mimo
  caresource
  nzbvortex
  calphalon commercial
  synkron
  simply
  scanpan
  contemporary nonstick
  care source

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Speaking about unison, one probably shouldn't forget about giganews.

Other search terms related to unison and their ratings are:
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