Kittydar (short for kitty radar), by Heather Arthur, is an open source, JavaScript library for detecting upright frontal cat faces. You can find its demo application at http://harthur.github.io/kittydar/ and its source code at https://github.com/harthur/kittydar.
Another detector for upright frontal cat faces was developed by Microsoft Research using the Microsoft Cat Dataset 2008. The detector is described in the following research paper, but no demo application or source code has been released:
Weiwei Zhang, Jian Sun, and Xiaoou Tang. Cat Head Detection - How to Effectively Exploit Shape and Texture Features, Proc. of European Conf. Computer Vision, vol. 4, pp. 802-816, 2008.
If you know of other work on cat detectors, recognizers, or datasets, please write to tell me about it!