Comment by blacksqr

Tcl has an "easy" threading mode where each thread runs its own interpreter, and a "hold my beer" mode where you can spawn threads within a single interpreter.

Tcl also has synthetic channels, so you can stay in easy mode but open a bi-directional read/write channel with the two ends in separate threads, with readable/writable events assigned, so you can do automatic event-driven information sharing between threads.

I don't know any other language that gives you options like that.