You can download all the realbasics, from about version 2+ but registration im unsure of. I got mine registered by some rather unscrupulous means. The version I downloaded runs on my Mac OS 8 machine (i think 7.6 is the earliest it will run on). And it compiles for PPC or 68K and itll run all the way back to System 7. the compiled apps may run on system 6 but i am not sure.

the only downside is the runtime is compiled into the application, which means the smallest the application will ever be is 352k i think.