Comprehensive Overview of OSM services
Wiki: List of OSM based Services
This list contains all kinds of special OSM map applications. Most of them are special maps with specific rendering parameters to hide unwanted items and/or to emphasize others or even show objects which are not visible on the regular maps. Note that some of this material is not free.
Tracking changes to the map
There are a few tools which allow you to find out if changes have been made to an area where you have been tagging and also about who made those changes. Of course you can use the editor and manually inspect every object (see "History of an object" in JOSM), and that's OK if you stumble upon a change during editing. But for "keeping an eye on your shop" there are more efficient tools available.
Openstreetmap Watch List (OWL)
OWL (OpenStreetMap Watch List) is a service that monitors, processes and stores changes in OSM data. You open the map just like you would with the regular [OpenStreetMap viewer], but OWL has an extra tool to get a list of all items in the current view which have been modified during the past ??? months.
Still in beta, but so far not bad. Of course there are many missing features; we'll see how development moves forward.
This program can be installed locally with a database and a frontend application, but can also be used as a web application.
Get notified via RSS when OpenStreetMap has been edited in your area. Draw a polygon on the map; when you’re done drawing an outline around your local area, send an email to the author. He will create an RSS feed.
Wiki: [OSM Mapper]
Mainly tools are oriented towards UK, but the MAPPER feature is also available for other areas. The data is updated once per day after midnight. You can set up an RSS feed to be notified when something changes in the area you wish to monitor. A tutorial for ITO! Mapper is available on SlideShare.
OSM Relation Analyzer
General Tag Checks
There are many quality assurance tools available to detect errors and inconsistencies in OpenStreetMap data. There is a lot of overlap between those tools, but the differences are interesting enough to use more than one tool on the same area. The ones below are my favorites.
Wiki: Keep Right
Link: http://keepright.at/report_map.php?zoom=11&lat=50.8159&lon=4.4412 The original link on the Wiki page centers the map on Vienna. This link centers on Brussels. You can make your own preferred starting point by editing the lat and lon parameter (and the zoom factor as well) in the url.
Wiki: OSM Inspector
Use the permalink feature to create a url which centers the map on your region of interest. OSM inspector has a large list of features to be checked. Interesting is also that you can use the OSM Inspector map as imagery layer in JOSM using the WMS access url. See my JOSM page for more details.