[roywiggins]

Another fun one is a Forth interpreter. I tried to make one in Rust once, I can't say I actually succeeded but it's fun to tinker with. It is simple enough that you can probably write a bad one in assembly without that much assembly knowledge.

[geon]

Or Brainfuck. It's fun and only takes half an hour or so.

[smcl]

Not sure why you're downvoted (people don't like swear words?). As a "my first interpreter" project Brainfuck is really quick, fun and could motivate you to explore the topic further.