Matthieu Brucher has released QtSimpleOverdrive, a freeware overdrive effect in VST plugin format for Windows.
Some interesting insight on how the plugin was developed is available on this page.
QtSimpleOverdrive is an overdrive VST plug-in with a Qt GUI. With a gain that can be selected between -40 and 40dB, the plug-in allows also different oversampling parameters. It uses the actual diode transfer function to solve the overdrive equation.
The source code will be available (under the GPL) in the future if there is interest in the plugin and its support. The exact way it works will be explained in a future blog post.
Download QtSimpleOverdrive by clicking here.