All the weapons and levels of the original, running on a 1MHz machine.
If you haven't played Super Crate Box, you should correct that deficiency post haste. Before making games like Ridiculous Fishing and the upcoming Nuclear Throne, the dynamic Dutch due birthed Super Crate Box, a fast-paced arcade title that's as endearing as it is frustrating. Sure, retro is in, but what if the pixels just aren't retro enough? In that case, Vlambeer has ported their classic platformer back in time to the Commodore 64, with Super Bread Box.
Vlambeer managed to keep an impressive amount of the original in the C64 conversion. It includes all the original levels and weapons, three new maps, 16 playable characters, and a chiptune soundtrack, all running on a 1Mhz machine with 64KB of RAM. The cut-down 16KB version is free to download, while the full 64KB version is yours for $3.22. "If you don't like paying for games," Vlambeer suggests, "checkout the Commodore Scene Database to see if anyone has managed to crack it" (spoilers: they have). These ROMs are intended for use in emulators, but will run on the real deal. You can even pick up an official (and quite collectable) cartridge for $48.56. There are also posters and a free soundtrack to further slake your game-lust.
Once you get up and running, you can even compete against the world using a unique high-score system. By entering your saved game code on the website, it will chalk you up on the global charts and even email you when/if you get bested.
Super Bread Box was originally made for the 2012 Game Development Competition, (which it won). Since then, Vlambeer has been working away at it, polishing it into the retro spectacle you see today. I can only imagine indie developers decades down the line porting their VR sims to the totally-retro Xbox 360.
Source: Super Bread Box