SpeedLimit is a (pf/post-10.10) preference pane for limiting your network
bandwidth to one of a couple different speeds — 768k DSL, Edge, 3G,
and Dialup.
It was adapted from the ipfw version here: https://github.com/mschrag/speedlimit
You should just be able to build the xcodeproj and install the
resulting build product .prefPane.
Binaries are available in https://github.com/jlongman/speedlimit/releases/