The 2.1.3 version of eXtCal is out. I remember to you that the 2.3.x branch is only for developpement.
You could find below the changelog for this version. The next developpement release will be for the Recurring event feature

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2007/10/07: Version 2.1.3
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- Add a file attachement feature to the module
- Add a "who's not going" feature
- Add a version checker (display a message if a new version of the module is out)


Install information :

Developpement version don't include upgrade script. You must install again the module if you have allready installed the module on your test server.