Dave Miller had posted a question about how to do this on long/wide boards, so I promised I'd post mine. I could not load the video, so it's all in pictures. I made this jig in 2002 when I needed finger joints on some 36" long edges. It is simple, precise, and there is no limit to the width of board it can do. The drawback is that it can only cut one finger at a time. For this video, I cut the finger joints for a 5 1/2" wide board, and it took me 7 minutes.
First, a few pics. The working face of the jig.
In between the two clamping boards is a 3/4" wide block. This fits exactly into the 3/4" wide notch that the router bit makes.
It should be obvious, but you use the same reference edge on both boards in the joint, so on one board you will be cutting into the face and out the back side, while on the other board you will be cutting into the back side and out of the face.
I set my bit to cut 3/32" deeper than the thickness of the board so that if I have edges tear out a little, I have excess to trim off when I'm done. Not a necessity, just my way.
Clamp the board to the bench and start from the reference edge, putting the jig in place with the spacer block tight up against the edge of the board.
Once I loaded these pics, I could not load any more, so, I will continue below in the comments.