Interesting light board build

Not a whole lot of details into this build, but the two bits I found interesting was the channel make into the 2×4 (router bit, but I don’t know any that are “T” shaped myself, so what did they use?  Or was it 2 different bits).  And the use of NEON Expo Markers so they light up on the board.

http://www.instructables.com/id/DIY-Lightboard/