Honestly, I thought in the past such lists of who uses which software was more of a narcissistic thing at worst and a thing for people, who just want to fill their website with text without any content at best, however I've found them quite helpful in finding new software, so I thought it might be helpful to somebody else, if I make such a list too. It goes like this:

I use Debian GNU/Linux on my desktop computer, Windows 7 (POSReady embedded) on my laptop. I'm contemplating dualbooting my laptop with Salix, but at the moment I'm quite content with my setup. I tried Devuan and Devuan-based distributions like Refracta Linux, but they always caused me needless trouble, therefor I'm fine with living with SystemD, as Anti-Unix as it might be.

For Mail is simply use Claws Mail. It's simple to setup and is much more lightweight than Thunderbird. Claws Mail is completely free/libre software and doesn't have unnecessary features like a built-in browser. For IRC, which I don't use very often, I use irssi on GNU/Linux and AdiIRC on Windows.

For music creation, I'm experimenting with Schism tracker and Milky tracker, both of which are very simple sample-based music creation programs. I'm not experienced enough to know which I like better, however I found Milky tracker to be easier to use.

The GIMP works quite well for my simple purposes and I think there is not much to say about it.