Trello sold to Atlassian. Stack Exchange and Stack Overflow sold to Prosus FogBugz sort of lives on at https://ignitetech.ai/softwarelibrary/fogbugz but it looks like one of those companies that buys software solutions and retains the minimum staffing to keep lights on.

Glitch isn't FC either, but to answer your question: is there anything left?

Yes, giant piles of money!

Fog Creek Software was renamed to Glitch, and they offloaded FC.