Maybe most interesting is Acorn's BBC Micro - it's a reasonable 8bit machine as is, but architected to act as a front-end to a bigger faster "second processor" - from Z80 to x86, and the very first ARM product.
These days, you can plug a Raspberry Pi into the bottom of your Beeb, and it can emulate a few second processors: a 274MHz 6502, a 100MHz Z80, a 6809, an x86, an ns32k, an ARM.
Then run GEM, or PanOS, or CP/M, and write in Pascal, Fortran, Lisp, C.