In a nutshell:
NM-4T, has 4 serial ports for WAN connections- i believe the T stands for T1
NM-1FE-TX has 1 fast ethernet port
NM-1E has 1 ethernet port
The NM-16ESW is a switching module with 16 fast ethernet ports and provides some basic switching functionality
References :
https://community.gns3.com/thread/4665
http://www.cisco.com/c/en/us/td/docs/routers/access/interfaces/nm/hardware/installation/guide/OvrNetM.html