The "Jointmaster" was first offered for sale in the 70's. (A decade earlier the name of this device would have suggested an entirely different purpose!) Described by its manufacturer as a "precision made sawing jig", these odd things turn up from time to time in my area. It's a die-cast tool with a stove enamel finish, which holds workpieces by means of plastic dowel pins in order to make cuts between 45 and 90 degrees. It originally retailed for £4.50. In it's Mark I form, it apparently won a Gold Medal at the 1972 International Inventors Fair held in Brussels.
The jig was produced by the Copydex Manufacturing Company, Ltd., with headquarters on Torquay Street in London, England. Copydex seems to have been best known as a manufacturer of glues, particularly a fishy-smelling rubber cement reputedly invented by someone with the improbable name of "Jim Bean Sherwood." Apparently, among other uses, actors applied it to ensure that their false eyelashes remained in place during long theatre performances. How they put up with the constant fishy odour isn't recorded.
Copydex went in for goofy product names, offering products such as "Chukka Cement," "Niftytape" and "Wundergrip." In another claim to fame, the firm was involved in a 1967 legal case, Seager vs Copydex, in which they were found guilty of appropriating someone else's patented carpet grip. The decision now seems to be an oft-cited precedent in British corporate law.
At some point, Copydex became Unibond-Copydex, and was then acquired in 1986 by the hoary German chemical company Henkel, which continues to market the fishy glue under it's original name. The Jointmaster, in contrast, appears to have been relegated to the dust bin.
From what I can determine from the instructions posted by someone online, the Jointmaster is something of a Rube Goldberg affair, requiring you to move the plastic dowels, insert a wedge, and otherwise over-complicate the sawing activities. Its functions can be better performed using other tools, leaving the actual Jointmaster to be best preserved as a curiosity.