Foursquare is becoming very popular now days,so its obvious that we need a foursquare widget for elgg.
So i divided the widget development project into two parts.
First is the foursquare_api which exposes the foursquare api functions and allows a great level of administrative flexibility.
To get it started you need to register a new application from foursquare at https://foursquare.com/oauth/ .
After that you need to include the client ID and client secret in the settings page.
Most of the other options on the settings page are self explanatory.

The api endpoints exposed are for checkins,todos and venuehistory

Demo at http://foursquare.heybuddy.in/

Remember this works only for elgg 1.8.