NETem emulates a network link, typically a WAN link. It supports bandwidth limitation, delay, jitter and packet loss. All this functionality is already build in the linux kernel, NETem is just a menu system to make the configuration user-friendly.
For more informations see http://www.bernhard-ehlers.de/projects/netem/index.html.
The image is downloadable from the releases area.
If you want to build it yourself, you need a linux system and install packer (https://www.packer.io) and qemu.
Then build the image with
packer build NETem.json
This fork modifies the project to support PCEngines ALIX and APU boards. This repo is a fork of Bernhard Ehlers work (https://git.bernhard-ehlers.de/ehlers/NETem) modified to boot & run on a physical system rather than a GNS3 VM.
Currently, there is an issue booting from internal SD Card on PCEngines APU boards & these must boot from a USB flashdrive. ALIX boards boot OK from internal CompactFlash.
The image is hard-coded to use 115200 baud on ttyS0. Low baud rates (e.g. 9600) make the menu system very slow to draw and make it painful to use.