MUI: Magic User Interface - the user interface libraries which a lot of Amiga software (particularly internet software) is based. Software built around the MUI classes can look better, have a more configurable UI, and have new gadgets.
CGX - Cybergraphics - a system that allows the Amiga's graphics to be retargeted to a graphics card. The other one often used is P96 (Picasso 96).
BSDSocket: Standard for networking. Hardly used it myself.
ELF: Don't know much, but AFAIK it's a format for executable files (programs).
Direct3D isn't there as it's M$ only technology, only on windoze. OpenGL is used on many other OSes (All Amiga-type OSes, Linux etc) and there is no point in having 2 3D APIs in a standard really.