I don't know if this type of jig already exists or not but i came up with the idea a couple days ago, half the time i use a jigsaw it is to cut boards or planks at length. And usually the cut is far from perfect.
So i made this simple jig, it works with any jigsaw, but the special rail base for the carvex makes it extra accurate as it slides on the rail of the jig. I also glued the part of an old folding rule on it, and it tells me exactly how far i am from the edge in case i want to make a stopped cut at a certain distance from the edge.
To make a cut you simply mark the length with a pencil, and position the edge of the jig on the mark, and cut! The jig also prevents tear out at the end.



I also drew a 3d jig that could be set at any angle, maybe i will build it later. but this one is real simple to make and stays square.

Crosscut jig for the Carvex jigsaw

looks good.  shame i dont have a carvex.
might work with my trion with athe rail attacment(dont have it so dont know).
handy for doing floors etc