Extended Basic and Mini Memory.
Extended Basic gave access to sprites. It quickly presented issues with timing (collision detection and lack of speed (compared with other Basics)).
Mini Memory. This was a relatively cheap way to get around Basic and Extended Basic, and get to the speed of most of the other popular computers. Was fun for a while. 768 bytes was like a limit, unless you got rather advanced (which the other computers really didn't require). I even got the 32 Memory Expansion, but overall view demanded I'd move to the C64.