It's actually not software at all. They use a glass surface between themselves and the camera with lights piped in the edges of the glass. They then use fluerescent markers to get the bright text effect.
Mirror the video image (or learn to write backwards) and viola.
"The lightboard itself is made up of a heavy duty frame, a 3/8” sheet of low iron glass (commercial name starphire,) and a string of LEDs to wrap the edges of the glass to shoot light inward to make the neon markers pop on camera."