CBM .prg Studio
There are many programs you can use do develop C64-games, the one I use is CBM Studio, you can code both with Basic and Assembly Language with this software.
You need an emulator to run your games, this is a great one.
DirMaster is a Windows-based GUI application designed to help Commodore enthusiasts explore and manage their disk image collections. Just drag and drop your prg-files.
High Voltage SID Collection
Do you need sid-music to your project, here is a large collection.
To play sid music files you need a sid player. With Sidplay2 you can get information from a sid-file that will help you to play it in your own code. Sid music files is not really a standard. The sid-files contain both player code and music data. The important data is the “Load Range” you need to load the music into this memory address, or it will not work. We also have the “Init address” so we can initialize the music playback routine. Last, we have the “Play address” to start the playback.
It would be very nice if you could move sid-files to a different memory location, fortunately there’s a tool for this, Sidreloc!