Maps on demo.transformap.co display (currently) an excerpt of OpenStreetMap data. Adding a new map is easy, one has only to change some lines with a new (overpass) query for the map wished, based on one of the current maps.
But how to get the data to display into OpenStreetMap? Some data will already be there (e.g. organic stores), others have to be added. You can use the iD or JOSM editors (short description here) for adding single points. If you plan to bulk import existing data from elsewhere, there is a How-To here.
If you have an idea for a new map, post a request in the category Demo Maps, or file an issue at github.