Forth is perhaps the tiniest possible useful interactive programming language.
It is a language that makes complexity painful, but which reveals that a surprising amount can be accomplished without introducing any. Forth is the opposite of “bloat”. If you've ever been like “Oh my God this Electron-based chat app is taking up 10% of my CPU at idle, what the HELL is it DOING, modern computing has gone MAD”, Forth is there to tell you that computing went mad decades ago, and that programs could be doing SO MUCH MORE with SO MUCH LESS.