Frowns is a chemoinformatics system written almost entirely in python. This software reimplements some of the functionality of the Daylight toolkits but it is not meant as a replacement. Daylight's code has higher performance, commercial support, more users, more complete testing, documentation, industry backing, and a cool set of people working for them. Plus, you can run PyDaylight located at http://www.dalkescientific.com/PyDaylight/ if you don't like the C API. Given that, you may want to use FROWNS if you; * are interested in the implementation details of chemical information software * want to teach same * have ideas that can't be implemented in the Daylight toolkit (new types of ring or aromaticity perception, support for different operating systems and platforms, etc.) * don't have the financial resources for the Daylight tools * just plain can't stand the idea of non-free software * have nothing better to do in your free time. Frowns currently includes the following features * Smiles parser * Smarts substructure searching (using the bindings to VFLIB) * SD file parser with SD field manipulations * Depiction for SD files with coordinates * Molecule Fingerprint generation * Several forms of Ring Detection available * Simple aromaticity perception * Full source code You can download the latest version of frowns at http://staffa.wi.mit.edu/people/kelley/ Or you can just skim the tutorial at http://staffa.wi.mit.edu/people/kelley/frowns.html Brian Kelley bkelley@wi.mit.edu Whitehead Institute for Biomedical Research