GoatTracker - This is a crossplatform C64 music editor.
DefleMask - An old-school game music tracker for an ample variety of systems.
1BITDRAGON - 1BITDRAGON is a user-friendly music creation software that allows anyone to make music without having to be an expert or have thousands of dollars of gear.
FamiStudio - FamiStudio is very simple music editor for the Nintendo Entertainment System or Famicom. It is designed to be easier to use than FamiTracker, but its feature set is also much more limited.
Jummbox - A modified Beepbox that have more stuff then Beepbox. It can be used just like Beepbox. The features of Jummbox is the same of Beepbox's features, but Jummbox have more stuff to offer.
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.