I just deployed the new version of RPG Playground at http://www.rpgplayground.com/, which allows you to store up to 8 levels per user. When saving or loading a project, a new dialog will pop up where you can select where to save or load your level. Your old level will be available at the first slot.
The next thing I’m working on is sharing your levels with others. This way you can show off your amazing creations :).