Crazy Boulders is written completely in BASIC (with exception of sound effects) and it comes with detailed walk through the code.
Access to full source code and tutorial is on my blog at:
https://www.8bitcoding.com/p/crazy-boulders_16.html
Program can also be downloaded here:
CrazyBoulders.zip- (19.11 KiB) Downloaded 354 times
Enjoy!