... The other is carboys. Seriously, who thought that design up? I love the Speidel fermenter I have now.
I have often wondered that myself. Based on a reasonably sound Wikipedia article (http://en.wikipedia.org/wiki/Carboy
), it appears that carboys evolved from jugs. There's also a hint about why 5 gallons became the standard batch size: "In Britain, demijohn refers to a 4.5 litre (imperial gallon) glass brewing vessel."
It hadn't occurred to me until your comment that carboys could easily go on my "regrets" list. I started with a bucket in a "starter" kit, moved to plastic carboys, then a couple years ago moved to food-grade buckets bought from an emergency-preparedness supply store (I drill the lids for gaskets and airlocks). They are inexpensive, easy to clean, easy to sanitize, and hold a good seal.