There are plenty of 'Marshall in a box'-style pedals around, but the Xotic SL Drive is probably the smallest we've seen.
Built in the increasingly popular mini style, with offset input and output sockets to save on pedalboard space. Two large knobs control the tone and drive action, and you also get a small volume knob for the output.
Based on Marshall's Super Lead and Super Bass amps, the SL Drive has four internal DIP switches to select various sound characteristics of both models.
If it's that late-60s/early 70s Marshall sound you want, the SL Drive will deliver, with the manual offering settings for Paul Kossoff and Ritchie Blackmore-style tones.
The Super Lead settings offer abundant top-end crunch, while setting the DIP switches for the Super Bass gives you low-end grunt and a more subdued top end, the whole lot cleaning up nicely with volume.