The German electronics magazine, Elektor [English], did these.
This one is intended for indoors and can be bought for US$1,200:
Elektor OSPV: an Open Source People Vehicle project
But before this one, they created one for outdoors.
And this one seems to be a DIY project:
Here’s an interview with the creator (in German):
Previously here:
Mike Cane’s xBlog 
Good to see these Segway posts. The dominance of the automobile probably overshadowed personal transportation.
Segways are fun. But I prefer the idea of human power.
Skateboards and scooters, for example, are great, also for fitness (travel A to B and be fit without thinking about it). But not much is done.
Cycles are OK. But you wanna carry your transport with a strap on your back (jump on a bus, train, or subway) like you can with skateboards, but not many adults use them, so little development in terms of A to B transportation.