For OS X, Apple offers a System Preference preference pane for download in their Developer Center called Network Link Conditioner, which is able to simulate low bandwidth, high delay, and packet loss.
How to download (from here):
First, you’ll want to get the Hardware IO Tools for Xcode. To do this, go into the Xcode menu, then choose “Open Developer Tool” and finally “More Developer Tools…”. You’ll be taken to Apple’s developer downloads site; you should download the “Hardware IO Tools for Xcode”.
Or (as of Jan 2014) go to http://developer.apple.com, Resources, OS X, Additional Downloads, then filter for Developer Tools.
This should be available for all registered developers and not need one of the memberships.