Go to OW2 Forge download page. Select the last eXo file for tomcat in the product section of your choice. It should look like: exo-product-x.x-tomcat.zip where XXXXXX is depending on the version you want to download.
Unzip that package under a path that does not contain any space (in windows).
Go to the bin/ directory that will be extracted. There, run the command :
windows: eXo.bat run
linux and Mac OS: ./eXo.sh run
Login as the administrator using the username "root" and the password "exo".