verses 
Coming across #furnacetracker and #sunvox in the same day, has made my day ...
Both are independent pieces of music composition software that are free to use. #freesoftware
Sunvox, as far as I can tell, has a lot of filters available that can be applied to instruments, and these filters can be programmatically controlled over time. I have not investigated Furnace too deeply yet but I managed to scrape together a melody in a pattern this afternoon.
As a former tracker enthusiast (composing via music trackers), it's awesome to see what projects have come about.
Link to SunVox's front page, which has many colorful screenshots, and tracks that can be played directly. They have compos (competitions) each year, it seems, and it's very cool to find a healthy community of artists doing their thing and learning from each other.