Yes - AA has a OW award that allows you unlimited segements based on miles. This can can be oneway in Econ, Biz or First. I have used it.

Using this award on AA, there are no restrictions on direction of travel but constraints include:
- You cannot stop over in the originating city
- YOu need to fly at least 2 other OW airlines in addition to AA
- You cannot connect through the same city more than twice
- The total mileage cannot exceed award mileage (understandable)

Other OW airlines have a similar award too.

American also allows open jaw domestic awards (at the same cost as Round Trip). The benefit over RT is that you are NOT required to return to the originating airport or city as some of the purchased tickets do. Many other US domestic airlines allow this too. Unfortunately it is not half of RT.

As others have noted here, the upgrades on AA are mostly now one way (half of RT).

Also, sometimes AA and others have special OW award redemptions. I don't know of a pattern here.