Want to double your productivity and be green at the same time? An Alberta, Canada company named Userful can get you two computers for the price of the one you already have, with its free software that can connect two or more computers to the same PC, more fully utilizing each computer, and reducing electronic waste by up to 80 percent.
 
"Computer hardware production and disposal is one of the fastest growing threats to our environment. Powering and cooling computers is an increasing contributor to global warming," says Timothy Griffin, President of Userful. "It feels good to help people around the world Go Green. In fact, last year our users more than doubled the previous year's savings, meaning that in the last 2 years Userful technology has eliminated the equivalent CO₂ of taking over 7300 cars off the road!"

The free giveaway started just before Christmas, but due to its popularity has been extended; it is being touted as an additional solution to help the environment for April's Earth Day celebrations.
 
If we examined our computer use, most of us would admit we only actively use a computer during a fraction of a day. The rest of the time it sits idle, eating up electricity and other resources. By expanding the use of each PC to two or more users, the cost per user clearly decreases. The Userful software can connect as many as ten people to the same PC box, leaving your expenditure in keyboard, monitor and mouse only.
 
Attaching 10 monitors, mice and keyboards to a single computer reduces CO₂ emissions by up to 15 tons per year per system and reduces electronic waste by up to 80%. Userful recently stated that in the last year their software has saved over 13,250 tons of CO₂ emissions, the equivalent of taking 2,300 cars off the road. 

More information can be found here. There are two free downloads available: a Live CD, which lets you turn your PC into 2 independent workstations without affecting any of the software on your hard-disk, and one for users already running Linux.
 
(Source: Useful)