The obvious answer is CLI stuff like bash, grep, sed, xargs, tar, etc. The shell suite found on Linux and macOS systems can contain code dating back to the 1980

The obvious answer is CLI stuff like bash, grep, sed, xargs, tar, etc. The shell suite found on Linux and macOS systems can contain code dating back to the 1980s. There’s some really ancient code in there. No need to change it. For UI apps there’s not much I use that’s that old.