Although this robot cropped up a few years ago, recent other farming type robots like the Tertill The Weed Whacker got us wanting to revisit Aquarius.
Aquarius is a greenhouse plant watering robot from Dorhout R&D. Utilizing a 30 gallon water tank it roams the greenhouse watering plants.
The robot is controlled by two Parallax propeller chips. Basically you dial in the plant pot size and set the robot line following.
David Dorhout is also the creator of Prospero Robotic Farmer.