Digitally controlled electronic loads are great for many purposes. First of all you can test batteries by discharging them with known current or measure power supply capabilities at high loads and so on. Jakub has been testing batteries and power supplies for some time, but his setup was manual. Eventually he decided to build more automatic solution and so he came up with electronic load Arduino shield.
The load is based on FET which gate is controlled by op-amp which allows to maintain constant voltage or constant current across load. The load can withstand 70W power dissipation with up to 10A current. Custom PC software allows reading voltage and current data also it accepts control commands like setting constant power and constant resistance modes. The FET on shield has to dissipate quite a lot heat so there is an active cooler installed which keeps temperature within safe margins.