OpenType.tools is an online toolbox that grew directly out of a free Windows application called OpenType Features Editor. Creative name, wasn't it? The OTFE was originally developed to help with some of the more tedious aspects of OpenType font development. Once the correct glyphs with the correct names exist in a font, several OpenType features can be automatically generated. That original Windows application can still be downloaded here.
An obvious shortcoming of the original utility is that it only runs on Windows. This website is an attempt to address that shortcoming and to provide a central location for additional tools as they become available.
All you have to do to get started is upload an Adobe Font Metrics (.afm) file. That file is parsed to display information about all the glyphs in the font and to automatically generate OpenType classes and OpenType features, and, when you are finished, you can download an OpenType features (.fea) file for importing into your font development application. Your project is isolated in its own location on the server while you work, and it is completely purged once your session ends. See the User Guide for more details.
Future updates will include an editor for editing the generated features, generation of FontLab classes (FLC files), manipulation of metrics and more. Please feel free to request any other features you'd like to see!