Brunetti are an Italian company who make some really great sounding amps and stompboxes. The Mercury Box is there overdrive pedal. Here's the description from the Brunetti website:
"Mercury Box is the new Brunetti overdrive/ distortion stomp box. A small metallic box holds together the qualities of the well-known CustomWork Mercury’s channel 2! It is endowed with “FET” technology to reproduce tubes behavior and dynamics as accurately as possible. Mercury Box is extremely versatile, you can move from clear and defined crunch sounds to hard rock “liquid” distortion which is always clean and never shapeless, very smooth and respectful of your instrument timbre, even at high gain levels. Controls are soft and sentive, but effective at the same time. They indeed interact thoroughly as in a real tube amplifier. Mercury Box arises from careful design and long lasting research of Marco Brunetti, and the outcome is innovative and technologically unique. It is not the upgraded clone of a well-know stomp box! These qualities make Mercury Box different, we are sure you will be impressed at first note!"
And a demo video of the Mercury in action (This is a clone built from the verified schematic below):
Here's the schematic: http://www.box.com/s/3ofp8pkkq9bov4uxkjrg
The chips are a MAX1044 or ICL7660 charge pump and a TL071 single opamp.
As the schematic shows the Mercury Box has a single op amp gain stage running into two jfet gain stages. Jfets do sound great as a clipping device. The whole circuit is powered at 18v via the charge pump, that adds headroom and dynamic range. All in all it's a pretty well designed circuit and it sounds neat too! One change I would make would be to replace the 22k drain resistors on the Jfet stages with 2 47k trim pots which would allow you to really dial in the sweet spots for maximum gain and sustain.
Here's the freestompboxes.org topic for reference: http://freestompboxes.org/viewtopic.php?f=7&t=9846