It doesn’t seem to exactly fit your description but Python Challenge (http://www.pythonchallenge.com/) has been incredibly fun and rewarding for me back in the day.
It’s a series of riddles that are meant to be solved using the python language. It’s really old now but I’m hoping that some library specific riddles are still relevant. Apart from those few, most of them should be language agnostic as well.
I’ve always wanted to create a similar thing to replicate the experience in JS but never gotten around to it.
Edit: oh also completely agree with most of the recommendations here. Particularly with TIS-100, Factorio and Human Resource Machine.
I can second the Synacor challenge. After writing the VM and completing the challenge, I ended up writing my own assembler and small compiler for it. Very fun.
It’s a series of riddles that are meant to be solved using the python language. It’s really old now but I’m hoping that some library specific riddles are still relevant. Apart from those few, most of them should be language agnostic as well.
I’ve always wanted to create a similar thing to replicate the experience in JS but never gotten around to it.
Edit: oh also completely agree with most of the recommendations here. Particularly with TIS-100, Factorio and Human Resource Machine.