Matthias from UNI64 is working on a test-cartridge for the Commodore C64 computer. With this test-cartridge you can do a complete system check even if the C64 does not have a video output. You can read the manual to see what all the features are.
Another new development is the uSTARTCart64. With the uSTARTCart64 you can load programs or games from a SD-card into the Commodore C64 computer. The uSTARTCart64 also supports TAPE loading.
A demonstration of the uSTARTCart64 on YouTube.