The best replacement for lync is skype.

The best alternatives to lync are rated as following:
★★★★★  skype
★★★★  communicator
★★★★  jabber
★★★★  cisco
★★★★  ocs
★★★  webex
★★  yammer
★★  avaya
★★  hipchat
★★  google hangouts
★★  live meeting
★★  lync basic
★  communicator mac
★  shoretel
★  cisco jabber
★  microsoft communicator
★  office communications server
★  asterisk
★  gotomeeting
★  moc
  pbx
  office communicator
  cupc
  sametime
  google talk

Your alternative for lync is not listed? Suggest!
Speaking about lync, one probably shouldn't forget about office 365.

Other search terms related to lync and their ratings are:
★★★★★ office 365
★★ edge server
★★ google chat
★★ adium
★★ asterisk
★ polycom
★ avaya
lifesize
trixbox
pidgin
You have in mind a companion for lync and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of lync in all years. Click on graph for more.
lync
skype
communicator