A full-screen slippy map with several different map views, a tile grid for debugging, and links to many other maps.
We found that we were using all kinds of OSM maps in our daily work, constantly switching between them - the one you had open was always the wrong one for what you wanted to do next! This "master slippy map" does most of the things we need, and will send us off to other maps for specialist tasks - while preserving the current viewport whereever possible.
Compare two maps side by side. Several OpenStreetMap and Google maps are available.
It is often interesting to compare how certain features are rendered on the various OpenStreetMap map offerings, and also whether the same features are also present on proprietary maps and aerial imagery. This side-by-side full-screen display lets us compare two map views and even has a slaved crosshair pointer for exact comparisons.
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.
The OSM Inspector has already become an invaluable tool for many in fixing relations, addressing, geometry or strange tagging errors. Its feature set grows with the project's demands - if something is hot in OSM, it will be on the Inspector.