Windows 95 here

j/k, Ubuntu on my main laptop (an old netbook), Windows 7 on my bigger laptop, which is mostly just for watching videos. I think one of my old laptops still has XP, but not sure, been some time since I booted it up. Might have replaced it with Ubuntu.
$this->bbcode_second_pass_quote('Subjectivist', 'I') used it up until I got a virus a few months ago, then I discovered after reformatting my drive that Microsoft no longer supports XP and would not update it from the factory version to the latest version I had been running. My old computer can't handle anything more advanced so now it is a door stop, very little of my software will run on it and the explorer version is so archaic it will not interface with most websites.
If you want to salvage it you could try Linux. There are distros that should work OK with older laptops if all you want to do is surf the Web.