I know of that website, it is made by a fellow OSMer, and while it's perfect for creating and editing GeoJSON, it lacks in simplicity of sharing maps (well, it depends on an external site for that). For example, MapBBCode Share maps can be embedded into posts on any forum or blog with MapBBCode plugin installed. Both sites were made with the same technology stack, though, namely Leaflet + Leaflet.draw.

And of course MapBBCode Share maps can be loaded in geojson.io: for example, http://geojson.io/#data=data:text/x-url,http%3A%2F%2Fshare.m... (replace zdjzk with map id).