A full-screen slippy map with several different map views, a tile grid for debugging, and links to many other maps.
Compare two maps side by side. Several OpenStreetMap and Google maps are available.
This tool offers different views on the OpenStreetMap data. It can be used to get a better idea how the data in the database looks like and it can point out omissions or errors.
This tool can calculate the estimated size of tiles in an area, allows to obtain bounding boxes from a specific area or calculate print margins.