ChemSketch is a freeware package available from
ACD/Labs and has announced over 350,000 downloads
http://www.acdlabs.com/news/chsk_ann350000.html
The file format is available at
http://www.acdlabs.com/servlets/UserAuth?
pr=chsk_fformat
Please contact me if you need more information
tony@acdlabs.com