BusyMac has released BusySync 2.0, an update to its software that synchronizes iCal calendars across systems. The new version's primary change beyond bug fixes and robustness is the capability to synchronize with Google Calendar. This addition overcomes a key weakness in the previous BusySync 1.5, which was the inability for a BusySync calendar subscriber to connect to a BusySync calendar publisher if the publishing system was located on a private network that lacked a publicly reachable IP address or required port mapping beyond a user's ability to configure.
BusySync enables you to publish a calendar on any Mac OS X 10.4 Tiger or 10.5 Leopard system on which BusySync is running. You can choose to let others subscribe with or without a password, and enable read-only access (like the standard iCal publish/subscribe model), or read/write access, in which a subscriber can add, delete, or modify events just as well as the publisher.
With support for the free, still-in-beta Google Calendar - which seems to be the release state for most Google Web applications - BusySync users can create an intermediate calendar hosted at Google that accepts changes bi-directionally. The Google Calendar acts as a conduit that both publisher and subscribers can access, avoiding the block of private networks.
BusySync 2.0 carries out this neat trick by using your Google account to pull down and push information to any Google Calendar you create. Because you can use Google Calendar to share your calendar with others using view or modify permissions, BusySync can pass events back and forth between iCal and Google Calendar. Anyone with whom you've shared your Google Calendar, and who likewise has BusySync 2.0 installed, can then retrieve and sync events with a local iCal calendar. BusySync has more details about Google Calendar setup in its online help.
BusySync 2.0 also works, sometimes, with Leopard's Back to My Mac feature. Back to My Mac creates an encrypted tunnel between any two Macs under your control. I had Back to My Mac turned on during much of my beta testing of BusySync 2.0, and BusySync revealed a lot of weaknesses in how Back to My Mac copes with other services trying to use its connection. (If you see Back to My Mac in BusySync's beta release notes, you can be sure I had something to do with reporting - not fixing - the bug in question.)
BusySync 2.0 costs $25 for each computer on which it is running, although BusyMac is selling it for $19.95 until 01-May-08 (and discounts apply for bulk purchases); a 30-day trial version is available as a 2.5 MB download. Updates are free to owners of a prior version of BusySync. Version 2.0 is also backward compatible with copies of version 1.5 running on your network.