The Malacandra Boost / Overdrive is a recreation of the Xotic AC Booster and RC Booster, two nearly identical pedals that feature a two-band EQ for independent control of bass & treble frequencies. The result is a flexible tone machine that lets you go from a clean volume boost to a thick overdrive.
Looking at the schematic for the AC & RC Booster circuits, you can see that it’s very similar to a Tube Screamer, starting with an input buffer and an op-amp feedback diode clipping stage. The two major topological difference are that the AC/RC circuit uses an inverting op-amp stage for clipping (the TS is non-inverting), and the Tube Screamer tone control has been replaced by a Baxandall stage with bass and treble.
With the Malacandra PCB, you can build either the AC or RC Booster by changing a few parts. Instructions are provided for each variant.