Our website provides a free download of Serenity 1.0.4 for Mac. The actual developer of this free Mac application is jmitch.com. The program lies within Lifestyle Tools, more precisely General.
From the developer:
Silence OSX notifications sounds, including Skype and Slack, with Serenity .
You may want to check out more Mac applications, such as Serena, My Living Desktop or Osmos, which might be similar to Serenity.