KMA Audio Machines Geminus Double Tracker

This pedal is very easy to use and does exactly what you expect of it: adding space to your guitar sound in a very realistic way, like the ADT used in Abbey Road Studio. This is not a simple delay, the effect is much more subtle than that and very convincing. You can also choose to modulate one or both outputs leading to more chorusy territory.
I use this pedal with two amps and the stereo effect can be fine-tuned using three controls: the large knob is used to narrow or widen the signal, the time knob is useful to increase the effect and the level knob to balance the two outputs.