My first computer was a ZX80 -- fond memories!
I liked it enough that my hobby Calculator app for Windows is now programmable in BASIC. It turns out that making a BASIC interpreter is pretty simple these days; there's a bunch of parser-generators to make it simple to program up the language, and modern computers are super-fast even when dealing with non-optimized code. In fact, the hard part is that people expect more GUI bits in the code, and getting those to all work took longer than the actual programming.
The downside is that it doesn't emulate any particular computer, and it's missing some nice features like "graphics" and "multiple statements on a line".