Now here are two funky stems I've come across. These are mountain bike stems.

The first one has a 0 degree offset, it places the handlebar directly over the steer tube. Would have to have some interesting effect on steering as it would eliminate the steering arc, where the center of the handlebar "circles" the steering tube.

The second looks the same, but it moves the bar to 20mm in front of the steer tube.

I'd never seen anything like them. And probably for good reason!