Independent Coasting System (ICS) by www.daVincitandems.com

Do a search of the archives using the terms ' daVinci tandem ' and you'll find several threads.

There are also a few other systems like this on the market, e.g., ATP Independent Pedalling System (IPS) which first appeared on Vision Recumbents tandems. Produced and marketed under license to someone else following ATP / Vision's demise a few years back. There's also a cruiser bike on the market with a jackshaft for ICS/IPS like crank action.