Mobile Crackmes
This is the repo where the WASP MSTG its crackmes sourcecode is stored. If you go here, you will spoil the fun for cracking the actual crackme's ;-).
The crackmes are actively maintained at this point in time. If you cannot start them on your device, feel free to file an issue or do a PR. Note that the OWASP Hacking Playground contains more testcases.