This app implements a very simple SOCKS5 server for iOS. You can use it to increase your tethering speeds when they are artificially limited; other uses are possible.
It is not distributed via the App Store because it'd probably get rejected.
Usage is simple: download this repo, git submodule update, and then build & deploy from XCode. Then set your system/browser SOCKS5 proxy to whatever it says on the screen (e.g. 172.20.10.1:4884) and away you go.
UPDATE: Because sideloading apps is a pain, I recommend using nneonneo/iOS-SOCKS-Server instead; it's a Python script that can be easily loaded into Pythonista for iOS and used forever without sideloading restrictions.