MosaicIt! allows you to create photographic mosaics. This means that a picture is divided into sections, that then are replaced with other pictures that have the corresponding average color.
It is licensed under the GPL, so you may download and use it for free.
By now, the user interface and the in-program-documentation are avaible in English and German. Help with translations is always welcome!

This picture e.g. will result in the following photographic mosaic: (note that only the top left corner of the resulting mosaic is shown in full resolution, as the complete mosaic has a size of 80 megapixels)
The programs user interface is designed to be simple and to guide you through the necessary process step by step. It is build on top of Nokias Qt framework, so that it features a modern user interface and the source code is platform independent. It was tested under Windows and Linux, but for now precompiled binaries are only avaible for Windows.