That one produces white flowers which open at night. The other common one that has the general aspect of the one asked about here is a hybrid of what has been called Nopalxochia ackermannii that is grown under the name of that actually rare parental species; as I remember it another name is being used now but searching N. ackermannii long enough will bring up the full story. Otherwise, the plant in question is one of among very many garden hybrid epicacti. There is a custom of calling all of these epiphyllums but that genus (Epiphyllum) is actually only one of several involved in the parentage of many of them.
That's what I thought too but according to the Wikipedia page on Epiphyllum oxypetalum there is a variation with crimson red flowers. Nevertheless the flower on this plant does not have the same look as the white ones normally seen so it's questionable whether this is E. oxypetalum.
The two common ones asked about repeatedly are the white, nocturnal Epiphyllum oxypetalum and the Nopalxochia ackermannii (and other names) hybrid grown as N. ackermannii. These are apparently popular pass-along plants or ones that by other means end up being grown by numbers of people who do not know what they are called. A red nocturnal cactus seems highly improbable, I have not so far seen anything about a red E. oxypetalum myself.
Thanks guys for helping to try and identify this plant. I'm not sure myself it looks like some kind of flowering cactus ? Its very old and I'm told this is the first time its flowered even though the owner has had it for many years.
The bit about "variation with crimson red flowers" is unreferenced, and can be dismissed as dubious, like much on wikipedia (and even referenced statements can sometimes be wrong too, if the reference itself is inaccurate).
Worth digressing into the reasons for this: red flowers have evolved for attracting bird pollinators (hummingbirds in this case), as they see red light better; birds are daytime pollinators, not flying at night. Conversely, white flowers are commonly adapted to pollination by night-flying moths, for which the white is a better (more conspicuous) marker. Red flowers (which appear black at night) won't get pollinated at night.