There are more robust calendar apps and more minimalist options, too, but iCal is the best option for Mac OS X because it falls in that sweet spot of providing everything most users really need without the stuff that you don't. Plus it's free, integrates well with OS X, and hardly requires a thought to use.
Platform: Mac OS X Price: Free (with OS X)
- Manage multiple calendars.
- Set alarms that can display a message, play a song and more.
- Create a to-do list with the Reminders feature.
- View your calendar to the day, week, month, or even year (which has a neat "heat map" view).
- Works with the Address Book application to easily access contact information and more when creating appointments with specific people or inviting them to a meeting/event.
- Works with several services like Google Calendar and Microsoft Exchange.
- Simple interface makes it easy to add new events, change event information and more.
- Automatically pulls birthdays from Address Book.
- Can handle time zone shifts in various ways so your calendar appears the way you expect when you travel.
- Quickly add events by typing in a phrase like "Dinner on Sunday with Grandma at 5PM".
Where It Excels
iCal is unusually compatible with third-party services for an Apple application. Generally Apple focuses on its proprietary technology and ignores what everyone else is doing, but iCal supports Google Calendar, Microsoft Exchange, Yahoo, the open source CalDAV protocol, and more. But the main draw of iCal is how easy it is to use and how little time you have to spend adding information to a given calendar. It makes a lot of smart assumptions so you can just add an event and be done with it. It even understands human phrases if you prefer to add your events that way. While iCal can't do your laundry and cook you dinner, once you have it set up you can pretty much use it without a thought. The best calendar app is one you really don't have to think about using.
Where It Falls Short
Google Calendar support could be better, as it currently requires you to add and set up your calendars in Google rather than use what you've got in iCal. This isn't hugely important, but if you're switching from local calendars to an online service it can be a bit of a pain. Additionally, iCal tends to fail to sync somewhat often. While this may not always be its fault, it provides many annoying alerts rather than simply dealing with the problem. The birthdays calendar has always been a nice feature, but the lack of alerts or ability to even add alerts renders it next to useless. In the latest version that comes with Mac OS X Lion, Apple added a new faux-leather skin. This is a purely aesthetic complaint, and you may not care or actually like it, but if you think it looks particularly bad there is a fix.
Microsoft Outlook tends to be the go-to alternative for people who don't want to use iCal or just want something designed to better integrate with Microsoft services. If that's your goal, or if you just want your calendar and email in the same place, you may prefer this alternative.
The Lightning extension for Thunderbird can keep your calendar and email integrated for free. If Thunderbird is your email client of choice and you also want a calendar, Lightning is a good solution.
BusyCal is the Mac calendar app for the user who spends a lot of time with their calendars. It will set you back $US50, but it offers tons of features you won't find with many other options on the Mac. It syncs with practically everything (or even nothing — it'll sync over LAN if you don't want to use a specific service), provides multi-user editing, offers weather updates, lets you add sticky notes, has more complex to-do support (including recurring to-dos), syncs with your iDevice, and much more.
Fantastical is a well-liked yet overpriced option on the minimalist side of things (our review). It puts a calendar in your menubar that's simple, powerful and attractive. That said, it operates as a front-end for other calendar apps like iCal, BusyCal and Entourage/Outlook. It does work with Google Calendar and Yahoo, but through iCal. If you want a free option that does the same thing to a lesser-extent, check out Calendar (our review). I use this and like it a lot.
Lifehacker's App Directory recommends the best applications and tools across multiple platforms.