DrHonz was feeling extra generous today and has also published the source codes of Manic Miner.
The zip file available contains the D64 image file with the game ready to be played, as well as all the assembler source code to be compiled using DASM.
As far as I could see, the source code is super well organized and full of comments. I believe even I would be able to rebuild it and maybe add some modifications of my own! How about you?
Link: CSDb