The yellow one looks to have a Firebikes logo on the side of the 'tank'. They're built by Sam McKay somewhere in the middle of Canada. Check out his website, he builds lots of cool designs and one-offs.
I built mine last year and put a lot of mileage on it. Top speed 50MPH with hall sensors. I ended up running it sensorless after burning one of the halls. This year I want to modify the frame and run full suspension- springer front end. rear- weld in some type of suspension trailing arm. Also want to reconfigure the seat. the sportsmann boardtrack seats are pretty amazing looking.
Looks like we both Googled the same search terms. I wrote a bit about boardtrackers, and there are a few here that I missed. Mind if I add them to the article?
BTW, the the CAD concept at the bottom of page 2 was produced and is for sale (roughly 100 frames exist). It is the Luna fat bike by ES member green machine. (add link here later, after the coffee kicks in)
Megavel from Mother Russia do some nice ones with Micargi frames.
I have so many pictures as I was researching building a board tracker/beach cruiser style E-bike and bought the Ruff cycles Tango + Porcuhu frames to start with my base. Just waiting on my parts to start my builds. Those guys at Megavel build some seriously nice ones In Russia.