BBC BASIC bot [beta2] on Twitter is lovely. You tweet a BBC BASIC program to it and it replies with an animation rendering of what your program would look like on a BBC Micro.
I sent it this:
which readers might recognize as 10 PRINT, the endless random maze one-liner for the C64. This program even inspired its own book – also called 10 PRINT CHR$(205.5+RND(1)); : GOTO 10 – about simple generative art.
You can run it in your browser thanks to the amazing JSBeeb.