The calendar that comes with your Google account is one of the best there is. You can share your calendar, or invite people to specific events. You can have your calendar automatically send you reminders of upcoming events, and even have it mail you a daily agenda.
The calendar works great for reminding you of upcoming things, even months or years ahead of time. You can have repeating reminders on a periodic basis, so you never forget a birthday or anniversary or any other event.
You are not limited to one calendar. You can create others for specific purposes and share those calendars so others can add and edit events, too.