Velleman Extradrive Overdrive K8111
A complete kit including everything needed to make the pedal shown here: Drilled case with decal, PC board and all parts, including high-quality Neutrik jacks. Similar idea to TS-type ODs, true-bypass, based on the NE5532 and 1N4148 diodes. The kit provides a three-position switch for choices of clipping styles, and you are clearly encouraged to experiment with different diode types.
Here are the schematic
and the Plain English build instructions.