I've long wanted a mowing robot, but have been pretty disappointed with what is available.  This looks like a promising project.

Maker Clemens Elflein devised OpenMower after being let down by the current generation of robotic lawnmowers. The only models he could find simply drive themselves in a straight line until they hit a perimeter wire buried in the ground, at which point they turn around a bit and then set off in another straight line. OpenMower is able to localise itself using very precise real-time kinematic (RTK) positioning, meaning it can mow a patch of grass much more efficiently.