BusyMac has released BusyCal 1.6.4, which lands just two days after the release of version 1.6.3. That update provided support for the Gatekeeper security feature in OS X 10.8 Mountain Lion, as well as a few minor fixes (a dock icon redraw bug on the MacBook Pro with Retina Display and a 403 error when syncing an iCloud WebDAV calendar). It also added support for the Daylite CalDAV server. Version 1.6.4 was released quickly to fix a Gatekeeper code-signing bug that caused some installation errors. ($49.99 new, free update, 6.7 MB, release notes)
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