The Internet Archive has a new software collection that includes thousands of games and programs designed for the Commodore 64 computers. And they’re playable in a web browser.
All of the programs uploaded have been “tested for at least booting properly,” but you may find some that don’t actually run. And many C64 games were designed for joystick input and maybe you'll have a tough time finding games that work with a mouse and keyboard.
Anyway, it’s still a pretty cool project that makes use of VICE, a free and open source C64 emulator to let you play games in a browser.