Look here, look here: the Know It Express will start nonstop service between the U Street Metro in Northwest Washington and the Park Slope area of Brooklyn (more specifically, Flatbush Avenue and Fourth Avenue near the Atlantic Avenue Long Island Rail Road station).
The cost is $25 one way and $45 round trip with a reservation, or $30 for walk-ups. For now, the buses will run Friday through Monday.
The bus leaves from Washington at 8AM on Sunday, Monday, Thursday and Friday. It returns from Brooklyn on the same days at 5:30PM.
According to the website the buses have free wi-fi, plug-ins and more leg room, lap top borrow service, special student fares, deals on local dining and free bike transport.
Nice.