METAGRAF is a graphical editor for creating figures in MetaPost. It is currently able to draw any kind of figure in b/w or color. METAGRAF outputs a MetaPost file which can then be run through MetaPost by itself or using TeX. The program is written in Java and is thus platform-independent.
Btw. I've tested the installer and it works, simply type 'jre -cp install.zip install
http://w3.mecanica.upm.es/metapost/metagraf.html
and for downloading:
http://w3.mecanica.upm.es/metapost/MG_1-0-5_Installers/install.htm
choose 'other Java enabled platforms'