My latest invention is Lotto Miner, a webapp where you can attempt to mine a bitcoin block in your browser and put the block reward directly in a bitcoin address of your choice. You can also mine on regtest, where you are more likely to succeed.
Try it here: https://supertestnet.github.io/lotto_miner/
Video demo: https://www.youtube.com/watch?v=1w8Fq8HejhU
The difficulty setting is low at first, but you can increase it til it matches that of the real bitcoin network. Raising the difficulty will take increasingly more work and, probably, more time.
The source code is: https://github.com/supertestnet/lotto_miner
I made this to help folks learn how bitcoin's difficulty assessment algorithm works and gain an appreciation for how much work goes into mining bitcoin blocks. Also, I'm not aware of any open source tools for creating custom bitcoin block templates on regtest, and this is a starting point for such a tool. The codebase is pretty small and since it produces valid regtest blocks, devs should be able to customize it to suit their regtest needs.
Try it out and have fun!