Mountain Tamer Triple adapter lets you use a smaller than 24 tooth chainring as your granny ring.
The MtnTamer consists of a machines aluminium spider which is bolted to the crank just as a typical 26/24 tooth chainring is secured to any old school crank.
On the machined aluminium spider you can use sprockets from a freewheel (I forgot which freewheel unfortunately), this one came with a 17 teeth sprocket which is as small as the Mountain Tamer Tripple Adapter lets you use.
I think you can run this as a quad setup with a standard granny chainring, so you could for example have 48/36/24/17 setup in the front, perfect for touring bikes.
But there is also a Mountain Tamer Quad adapter specially made for quad front ring setups.
IIRC these where also available in anodized purple BITD.
With the advent of internal front shifting maybe the days of multiple chainrings are soon long gone, but the Mountain Tamer Tripple adapter is a tried and true way for you to tame those long climbs up the mountains or a way for you to build the ultimate uphill bike.
Uphill was also known as a long time forgotten sport of MTB where you rode a bike up a mountain.
Sold for 15 euro!