I just bought a used MOD Duo. And although I created the design of user interface and the plug-ins back in the days and have written a good share of the effects available I actually have never had my hands on the real thing. Just played around with it for a while and I have to say it's absolutely stunning! This one will be used by my bassist, so it seems I have to get a second one for the drums - because I'm simply flashed.
Concept is the following:
Inside the device is an ARM board running a stripped Linux, optimized for audio processing. This runs all the LV2 plug-ins available under Linux at a very low latency (either 2 or 5ms). In production it is running as a stand-alone device, controllable via the knobs and buttons on the device (or other controllers available, even DIY ones). You can connect a computer via USB to get access to the user interface. From within that you can freely arrange and wire up all those fancy plug-ins until you run out of processing power. Those pedal boards can then be saved and arranged in banks to be recalled from the devices controls.
Plug-ins can be installed from an app store in seconds through the UI as well - all free. Same is true for pedal boards: there's a huge library of user boards available and installable through the UI. Missing plug-ins are installed automatically together with the pedal boards from the library. All plug-ins parameters can be automated or controlled by the controls on the hardware.
You can use line signals, instruments like guitars or basses and even microphones as input directly. It comes with 2 ins and 2 outs which can be used independently. So for drums I'd plug my snare and kick to add some fancy effects.
There's all effects available one can imagine - lots of reverbs and delays, dynamics (compressors, gates, limiters), distortion (saturators, all those well-known guitar effects, bit crusher and much more), modulation (dozens of choruses, phasers, flangers, ring modulators etc), lots of amp and cabinet simulators, equalizers, enhancers (exciter, bass enhancer, ...) and much much more - as I said, mainly all plug-ins available for Linux OS.
After you set up the device unplug the computer and use it as stand-alone with the two displays, the two (pushable) knobs and the two buttons.