A search tool to help you find specific points of interest and street names, but the search is limited to the data provided by OpenStreetMap. This data is more limited than that available in Nokia Maps or Bing Maps and the coverage quality varies greatly from city to city. The maps themselves are decent, similar in quality or better than your average A-Z map. OpenStreetMap data tends to be strongest in major metropolitan areas, which greatly benefits this series of apps. In some cases it can be more up to date than the data provided through the major map data providers (Nokia and TomTom).
The major limitation of the City Maps app series is that the maps are non-navigable; that means it is is not possible to plan a route from A to B. As such the apps might be best seen as a replacement for a paper-based street map, rather than a full mapping and navigation smartphone app.
Nokia Maps and Bing Maps both provide city maps (and navigation) for free. However, they do require a data connection and the map style may not be to everyone's taste. Silverdex's City Maps provide an alternative and have the advantage of working without a data connection (assuming you've already downloaded the map data). That may offer enough of saving, especially when roaming outside your home network, to offset the cost of the app.
City Maps are a collection of offline maps that you can download on to your device. You do not need a data connection to view the map and so it can be used abroad without experiencing additional charges or where there is no signal.
When you purchase and install a City Map, a large map is download onto your device which can be navigated by using pinch-to-zoom and finger panning. The map includes many useful points-of-interest such as restaurants, hotels, ATM machines, shops, stations, bars, cafés, etc. It also includes a search feature which helps you find streets and points-of-interest.
City Maps (e.g. London) can be downloaded from the Windows Phone Marketplace. No trial is available and each city costs £0.79 / $0.99 / €0.99. You can see all of the 150+ City Maps apps listed here.