> Boom is a simple volume booster that lets you boost the volume of
> your Mac and your music files.
>
> Using Boom is simple. You know the ways to change the volume of your
> Mac. Boom provides the same easy access to boost sound.
>
> From the videos on YouTube, Hulu, your favorite music playing on
> iTunes, to voice applications like Skype, iChat and your favorite
> Games, Boom can boost them all. Add to that the ability to boost
> audio and video files, you have a booming addition to your Mac.
>
> So start booming and blow away the silence!

[Archived site][1]

Boom 2 for modern Macs can still be purchased from Global Delight's
website.

#1: Boom 1.1.0 (2011) (Universal) (10.5.8+)
#2: Boom 1.3.0 (2011) (Intel) (10.5.8+)
#3: Boom 1.9.1 (2014) (Intel) (10.5.8+)
#4: Boom 1.9.3 (2015) (Intel) (10.8+)

Compatibility
Architecture: PPC x86 (Intel:Mac)

PowerPC:
PPC G4 1.83 GHz and above
1 GB RAM

Intel:
Intel Core 2 Duo 1.83 GHz and above
2 GB RAM

  [1]: https://web.archive.org/web/20110511010543/http://www.globaldelight.com/boom/index.html