I contribute my skills to a number of online communities and share my knowledge through contribution, management or advice. You can browse a number of them here.
OpenStreetMap (OSM) is a collaborative project to create a free editable map of the world. Created by Steve Coast in the UK in 2004, it was inspired by the success of Wikipedia and the predominance of proprietary map data in the UK and elsewhere. Since then, it has grown to over 2 million registered users, who can collect data using manual survey, GPS devices, aerial photography, and other free sources. This crowdsourced data is then made available under the Open Database Licence. See my contributions to this outstanding project at https://www.openstreetmap.org/user/ElNumbre/