I still use an upgraded Newton Messagepad 2000 mainly for notes and journal entries. 99% of the time I remember things better with a kinesthetic act, so it's filled with a bunch of notes and other scribbles just because I needed some kind of movement (in this case a stylus on screen) to retain it in my head.
Alas, with how clunky it's been trying to sync with the rest of my digital life, it's currently in Dual-Carry status with a Note 8, with eventual retirement as a conversation starter on my bookshelf.
I have a 1999 iBook clamshell that my daughter now uses for school. It has been upgraded with more RAM and I replaced the slow HDD for a Compact Flash card so it's probably the fastest clamshell of the world...
For basic tasks (homework assignments, simple image/video editing, light browsing) it's surprisingly usable! The only downside is that I had to create a separate, unsecured WiFi network because the original Airport card doesn't play nice with modern security protocols. Oh well.
Apple 30" Cinema Display (2560x1600, 60Hz, dual-link DVI) that I bought in 2005 and have lugged around with me to jobs and homes since then. Still works perfectly.
Might not be as old as some others as I have throughly modernized this January but https://github.com/ddev/git-blameall is very useful: this is a tool similar to git-blame, but it shows every line that was ever in the file, along with information about when it was added or deleted.
Alas, with how clunky it's been trying to sync with the rest of my digital life, it's currently in Dual-Carry status with a Note 8, with eventual retirement as a conversation starter on my bookshelf.