MS-DOS 6.22 and Windows 3.11, and the productivity (Quickbooks 5, Microsoft Works) and game (Sierra Hoyle Card Games, mostly) software on them.

I bought the original machine in 1995 and Quickbooks 3 shortly thereafter. When the year 2000 came around the "fix" Intuit provided was a free copy of Quickbooks 5, the last version to run on Windows 3. Not really a huge improvement on v3, and in fact broke some useful features - finding things in lists, for instance - but it still adds and subtracts just fine. Whines from time to time about wanting to contact the mothership for updates.

When the CMOS battery finally died after 20 years or so I found that instead of a button battery, it was a big rectangular block soldered to the mainboard. I couldn't replace it, so I took the hard drive out and installed it in a build I'd made around 2000. The CPU on that mainboard runs much faster, 2400 MHz instead of 100. While Quickbooks and Hoyle Card Games never hiccuped, MS Works sometimes doesn't "catch" when I try to start it, forcing me to reboot. Better than Corel Wordperfect, which now refuses to start at all.

Very interesting thread.

Regarding which 6502 software I use often. I was actually a bit shocked since the last two years I haven't actually used any 6502 software. Towards the end of lockdown my day job became more busy and I couldn't get around playing with 6502 stuff.

Earlier on in the lockdown, though, I used the ROMS of the C64 and the Game 'Dan Dare' quite bit to test parts of my C64 FPGA design.

On a Windows PC I tend to use plain vanilla 'NotePad' quite a lot to jot down my thoughts when solving problems.

I also use a version of Vivado that is a couple of years old.

Sadly I wrecked my last c64 the year before last (actually that's what got me started trying to build a new 65 based computer) so I don't use any 6502 software at the moment.

For PC based software: I still used Adobe Photoshop 7; and run the odd emulated arcade game in MAME.

Everything else I run tends to be latest and current. ... not a particularly exciting post