This tutorial by Mylenium will show you how to create a fully animatable diagram with a few expressions and some thinking around the corner. While there are other techniques to create such graphs manually based upon Masks or the Write-On effect, this one has the advantage of being quite flexible and allowing last minute changes once you have the basic template. It cannot save you from buying dedicated software if you need things such as XML import or more variations of the look, however.
Adobe After Effects
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