The idea is simple: you want to have 2-way sync between your iCal stuff, your Google calendar stuff and any local Macs. Simple, yes, but so complicated very few do it right. There's MobileMe if you stick with Apple's solution, and Google Sync if you are a devout Gmail user, but there's still the issue of 2-way sync when it comes to subscribing to calendars. And let's not forget that MobileMe data has to go to Apple's servers when you could sync between computers locally, right?
BusySync fixed all of this for me. Local Macs used Bonjour to connect and sync, and my Google calendars appeared in iCal with seamless 2-way sync. Calendar data is a tricky thing, and the last thing you want to happen is to have all your appointments and reminders vaporize in an instant. However, I can report that BusyCal doesn't nuke anything. Like 1Password, you can always go back to Apple's default tools.
Enter BusyCal as a full application. Why replace iCal? I have to admit, I was a little skeptical. BusyCal is iCal evolved, providing a better experience in several key ways. First, one feature I have longed for in iCal is a list view, a simple top-down view of every appointment within one or more calendars. This makes is much easier to make decisions about nuking an entire calendar at once, and is very handy if you have too many calendars or no time to go month by month, scanning for the right color or words. Second, there's a lot more UI finish to BusyCal, with easy-to-access panes for adjusting event info. Even Snow Leopard's iCal, which reduced the number of clicks it took to edit an event, doesn't allow you to edit events this easily. For you UIX geeks: a frickin' non-modal floating window OR an embedded entry window. What a concept!
Adding to the ease there are some nifty extras, such as seeing your to-do's grouped logically or moon phases and the week's weather in your calendar. Of course, these options are all configurable, as is the Google sync option. More than nifty are features like rich text, adding images and stickies to events, a more advanced alarm window, and offline editing. BusyCal has, in less than 24 hours, become a mission-critical application for my Mac, both at home and at work. If you are a BusySync user, you can upgrade for $10, or buy new for $40 (per computer). It is well worth the price if you deal with lots of calendars.
Be sure to check out our previous coverage here and here. I would also be remiss in pointing out Spanning Sync, which also syncs Address Book with your Google contacts, but works a bit differently.