https://github.com/openstreetmap/openstreetmap-website/ a rails app basically and a way to import the planet back into the database (not sure how to do this but I think its possible).

You wont have any of the history, and no users info etc, but you can edit and if you have tile server set up can serve tiles from it as well.

Far better though is to import the data into PostGIS (the rendering database) and edit and add that way with a desktop gis.