Modview can be used to:
-check out if your custom model/skin shows up right
-check regular models/skins
-check for tags to show up in saber models
MD3view (also in the tools dir.) can be used to convert MD3 models to ghoul2 (.glm) models, which are used by Jk/JA.
AS you will notice, the last one is very usefull for those who make custom models etc