SunVox is being actively developed by Alex Zolotov, also known as NightRadio. SunVox is what is called a tracker-type music sequencer software.
|A screenshot of SunVox 1.6.|
A tracker's musical interface is traditionally numeric: both notes and parameter changes, effects and other commands are entered with the keyboard into a grid of fixed time slots as codes consisting of letters, numbers and hexadecimal digits. Separate patterns have independent timelines; a complete song consists of a master list of repeated and concatenated patterns. (taken from Wikipedia)
Almost all other trackers (OpenMPT, MilkyTracker, Little GP Tracker) take this line-based approach only. However, SunVox also has a powerful pattern editor, much like a more professional audio workstation program like Reason or Fruityloops. In this editor, a user can put down any number of patterns on a grid (or not on a grid, if they so choose) to make up a song. This approach puts a much needed refreshing spin on tracker-based music creation, making it far easier and more fun to put together a song that you like.
SunVox also is a modular tracker, which means that rather than the user simply putting specific effects onto a pattern, the user can run sounds and music through effect modules to be processed. An example would be putting a bassline and a lead synth through a filter module and then connecting that to the output. This way, you have complete control over how synths and samples sound at each stage of the process. If you feel the need for free cross-platform music creation, take a look at the homepage here. Also, I've started a SunVox song archive where users can post songs for everyone to hear and download. You can check it out here.