The best replacement for growl is play nice.

The best alternatives to growl are rated as following:
★★★★★  play nice
★★★★  notification center
★★★  leer
★★  smokescreen
★★  snarl
★★  roar
★  os x notifications
★  tail whip
★  play nice pokemon
★  hiss
★  notification
  scream

Your alternative for growl is not listed? Suggest!
Speaking about growl, one probably shouldn't forget about beep beep.

Other search terms related to growl and their ratings are:
★★★★★ beep beep
★ apple mail
You have in mind a companion for growl and it is not yet here? Propose!



Google Trends

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growl
play nice
notification center