Both Festool and Makita used to advertise their saws as capable of this (although AFAIK Makita haven't ever made nice clamps like those in the video). In most British houses it would be tricky as floors and doorframes are often not true - Once you get away from the old colonial states, American new build is often on greenfield sites and commonly of wooden frame construction, so it makes sense. I am very tempted to get a pair of those clamps asn they would be useful for all sorts of rail saw operations. And next time I am door trimming, I'll try that first.
@ Andy Hamilton: Tracksaws ("plunge saws") replace many of the traditional functions of circular saws. They are safer, in many instances faster too, and the quality of cut is superb. What's more, you can ditch a lot of jigs: I have one Systainer for the saw, spare blades, mains extension, clamps etc., and a bag with 2x 1.4m rails in it (which is well-padded and can tuck-in anywhere in a van, estate car, whatever). My saw is 110V so no issues on-site either. The dust extraction is also superb.
I gave my traditional circular saw away, and don't miss it. Anyway, the Makita has the fittings for the traditional circular saw fence/guide if that was ever needed. They are so good that (now the patents have expired), most tool manufacturers are copying the premium brands as fast as they can. And now they are cordless, too. Mine is my most used power tool, after my cordless drill. I think it's made in the UK too.
