What is your problem/koan/TodoMVC to try out programming languages?

For frontend development on the web TodoMVC is an established example to test programming languages with; whether it is performance, ease of implementation or whatever your metric is.

But not everything runs in the browser, and whether you are looking for the most enjoyable programming language out there or you want the most concise or ... you need a project to kick the tyres of a programming language. What is yours?