Ditto: http://geojson.io/, https://github.com/mapbox/geojson.io.
There's a few npm modules for the command line, so you can do the likes of `geojsonio < some.geojson` or `togeojson my.{kml,gpx,…} | geojsonio`
geojson.io uses gist.github.com as a data store: http://geojson.io/#id=gist:anonymous/92dd314a02c072d658f4&ma...