I have a good old ThinkPad that I have had for a long time. It is still good (ThinkPads last forever) and I want to do some stuff with it. What Linux distros, software, and general technical stuff should I do with it to give it new life?

It's a T420 btw, also I booted Tails on the thing.

The retro kid in me wants you to put XP on it and use it for old games, but from a more practical standpoint I would suggest something like EndeavourOS with the liquorix/zen kernel to try and cut down on memory usage, while still having a very functional and versatile system not hindered by it's age.

KDE runs surprisingly well on older computers despite it's eye-candy, but if you want to maximize performance and nerd factor then I would recommend DIY'ing your desktop using Openbox.

Unless you got that model number wrong, the T420 is not an old machine, only just over a decade of age. Any Linux will do as long as you aren't running GNOME with it.

Yeah I had a T510 before I gave it away and honestly save for the slow hard drive it was a competent little machine for web browsing and such, and it still is, if you upgraded the RAM slightly and ditched Windows. It doesn't get bad until you go into the Core 2 Duo or weaker circa 2005~.

Just don't expect to be playing games on it though if your OEM didn't give you a discrete video card. Intel HD Graphics from this time period were terrible. Some of these ThinkPad models came with GeForce cards but then sometimes you got a bad one from some office and at that point you've got a homework machine.

Damn Small Linux just had a new release after 12 years, at ~700MB and running off of only 87 MB RAM, could be good for running on older machines.