Sound Transit's Central Link has opened: http://www.soundtransit.org/
The 16-mi / 25-km line runs from Westlake in downtown Seattle southward to Tukwila International Blvd.
Some extensions are now being built, southward to Sea-Tac International Airport (late this year) and northward to Washington University (2016). The line runs in a tunnel between Westlake and King St, and it will run in a tunnel to that university.
There are plans to extend it further northward, and also eastward from downtown Seattle to Mercer Island, Bellevue, and Redmond. It may possibly be extended to downtown Tacoma also.
Sound Transit also has a short light-rail line in downtown Tacoma, and its Sounder commuter trains running Everett - Seattle - Tacoma. There are plans to extend the latter further southward, to Lakewood; that will require construction of a short connecting line between D and M Streets in downtown Tacoma. But if it is built, it may enable the rerouting of the Amtrak Cascades trains to that line and away from its current coastal route to the north and west of Tacoma.
So Seattle is catching up with its neighbors to the north and south, Vancouver, BC and Portland, OR.