I can't have any kind of computer now without f.lux on it, since I've gotten so used to it. Any desktop at least, since it wasn't until last week that I actually installed it on my tablet (usually if I'm using my tablet at night, it's to listen to things while falling asleep, so I won't usually be looking at the screen).
As for what I do to relax, I'll listen to videos if I think they'll actually put me to sleep. If I just need something to do to pass the time until I'm calm enough, then I might just get up and listen to music, play a game, work on something...
And if it's bad enough and nothing else has worked and if I need to get to sleep now, I just kinda force myself to lay there without fidgeting and clear my mind. Focus on the sound of my floor fan, at the very least.