Núcleo is a toolkit for exploring new uses of video and new human-computer interaction techniques. Rather than performance and reliability, Núcleo is focused on the ability to support rapid prototyping and incremental development of video applications. This approach contrasts with many of the research themes usually associated to video in the Multimedia or Network communities such as compression, transport or synchronization. Núcleo runs on Apple Mac OS X and Linux and is freely available under the GNU Lesser General Public License (LGPL).