The Salsa Anything Cage is designed to let you carry more stuff on your bike. It attaches with three bolts, to specially-designed eyelets on the forks of bikes like the Salsa Fargo, Surly Moonlander, Surly Ogre, Surly Troll, Surly ECR, and many others.
If your bike doesn't have the special 3 eyelet pattern, other bottle cages are a better bet.
Comes with two straps. Cage is 149g, weight limit 3kg.
This is the HD (plastic) version - there's also an alloy version.