I apparently enjoy reinventing my own wheel(s) many times over.
https://github.com/ahungry/ahungry-map
The latest update is a clojure based client (so it'll run anywhere JVM can run, without headaches of C++/SDL portability).
Although, my first version (Common Lisp p99-patcher map program) used the browser to render, and API calls to track friends/other users, so you could actually see your fellow map users on the map and meet up with each other etc. easier.
Maybe I should add that to the clojure one (the c++, probably abandoned)