QBooru
Simple viewer app for most Booru Sites, coded in Qt C++
... and 5-8 columns. The recommended size is 3*5, as it fits perfectly the smallest window size.
Search tab example : http://puu.sh/cK0pj.jpg
Users can change nearly all the parameters through the Option tab, or by editing the configuration.json file. Boorus can be added, edited, and deleted through the Booru tab in the software, but they can also be edited manually in the configuration file.