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)
Fun Way to Send Attachments in Mail
If you're working in a file that you want to attach to a message in Apple Mail, you can transfer the file to Mail easily: From the title bar of the file's window, drag the little proxy icon to Mail's icon on the Dock. Your Mac will make Mail the active application and open a new outgoing message, with the file attached.
(If your icon won't drag, the file probably isn't saved.)