Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
MuseScore.org - Create, play back and print beautiful sheet music with free and easy to use music notation software MuseScore. For Windows, Mac and Linux.
Reaper - Reaper is a focused digital audio workstation (DAW) developed by Cockos. In the creation of the software, the digital audio technology company intended to make audio editing accessible to the masses.
Finale - Finale, the world standard for music notation software, lets you compose, arrange, notate, and print engraver-quality sheet music.
FL Studio - Image-Line's FL Studio, now on it's 12th version, is a well-known music production suite and the most popular beat processor on the market, due no doubt to its longevity. Read more about FL Studio.