most old software, honestly.
there's a reason for this, i suspect. before always-on internet was a thing, you had to actually make a program people would want to download, and one that wouldn't — couldn't — phone home and update constantly. it had to be actually feature-complete, or close.
ms paint, xp-era, has a host of keyboard shortcuts and simple features. for line or pixel art, it's impeccable. it does exactly what you need, it's worked fine for years. the old windows calculator, before the modern ones, similarly. old simple tools like metapad (notepad replacement) worked great.
when the era of auto-updating software started, a lot of that ended. just shove out garbage and patch it up later. let users be your beta testers. ship a bunch of weird changes and incomprehensible a/b tests to constantly "redo" things so that long-time users get confused and nobody knows how shit works any more.
it's hard for me to pick out particular ones because it feels like there were separate eras of software development for that reason.
(on some level, it was also about resources; 10 years ago, you couldn't count on people running 50 instances of a bloated web browser just to do basic shit like run a calculator.)
but yeah. the 95-to-XP version of MS Paint probably fits that. it's smooth, it's easy, it works, for a basic "draw shit and paint pixels" program it is miles ahead of even the newer ones.
