If you like using Google Calendar, but you also have an iPhone, BusySync can make sure they stay friends.

iCal is pretty capable on its own, and it’s convenient to push your calendars to MobileMe so they stay synced with your iPhone or iPod touch. But when you subscribe to others’ calendars, iCal puts them below your own calendars, in a separate Subscribe section. Since MobileMe and iTunes can only sync your top-level Calendars list to your iPhone, nothing from your subscribed calendars shows up.

BusySync moves subscribed calendars up to that top-level Calendars list, so they’re pushed to MobileMe, or available for iTunes to send to your iPhone. The app can keep your Google Calendars in sync with iCal in the same way, so your Google Calendar events can be pushed to your iPhone too. You can even share those calendars with other BusySync users on your local network via Bonjour—true sharing, with read and write access, not just a read-only subscription.

Residing in System Preferences, the app consists of six tabs. The General tab has a Start/Stop button—BusySync launches at startup and runs in the background, but you can stop it from here. The Publish tab shows all the calendars in your top-level Calendars list in iCal, and lets you publish them as read-only or read-and-write calendars for other BusySync users, with optional password protection. The Subscribe tab lets you subscribe to calendars being shared by other BusySync users on your network, and has an Add Remote Server button for syncing with BusySync-enabled Macs over the Internet (which requires some tinkering with your router settings, so it’s actually easier to use a Google Calendar as the go-between).

The Google tab is where you sync your iCal calendars to Google Calendar, or have your Google Calendars show up in iCal. Since Google Calendar supports alarms (pop-ups, SMS texts, and emails), those can ride along. But Google doesn’t have To-Dos, so if you use To-Dos in iCal, those won’t sync to Google. Finally, the Reset tab can restore your iCal database from BusySync’s automatic daily backups, or just reset the sync history, and the Log tab lets you keep an eye on things.

Leopard users can keep their information encrypted with SSL, a nice touch. The only drawback is that you need a separate BusySync license for each Mac you want to keep in sync, but you get a discount on five licenses or more. (Merely keeping iCal synced with Google Calendar is a one-license job.) The FAQ and User Guide on BusyMac’s site do a good job of spelling out the myriad syncing scenarios BusySync can handle, and more help can be found on the official forum or even by emailing the developers themselves.