Just a minor update on AcmeCal. The new feature is the Import/Export frameworks. At the moment I can export to an YAML stream of the internal representation and import from the same YAML string or from a subset of the iCal standard. At the moment no unfolding of recurrent events take place. Calling it a framework might be a bit of a stretch but support for other formats should be as easi as handling these formats.
To prove that everything is to be considered unstable I renamed the scripts from acme-(\w+)cal to acmecal-$1.