A very similar jig was patented in Canada a few years ago.
When put on sale it soon became the biggest selling power tool accessory in North America.
It's made of plastic and is meant for circular saws but can also be used for routers.
One slide is fixed at 90° and the other is adjustable for different saw or router bases.
The only real difference with the same jig many have made is the addition of an adjustable mitre fence so almost any circular saw can do the same as a radial arm saw.
http://www.macboard.qc.ca/indexe.html
I made my own out of some chipboard and softwood rails after seeing the MAC board demonstrated.
I then started making one with a much longer back fence so I could fit stops for repetitive housings.
A bad injury 12 months ago put everything on hold until I'm fully repaired.
This inactivity has allowed me a lot of thinking time so the workshop (garage) will be cleared then refitted to give more working space (therefore safer) with all gardening tools being moved to a new shed to be built.
A carport like covering for the rear of the house will allow all the tools to be kept out of the rain while new work benches and tables are made to suit all the power tools I have accumulated over the last few years.
I'm really looking forward to the clearout so I can put all power tools i their place to simplify their use.