My personal assistant (aka my smartphone) keeps me informed and organized. But while the calendar utility that comes standard is functional, I've discovered there is a myriad of more versatile and powerful calendar apps well beyond any phone's stock app. With so many to choose from, I've narrowed it down to some of the best for Android, iOS, and Windows Phone 8.
iOS
Left: Week Calendar - Right: 2do: Tasks
Week Calendar
If you're the type who tends to view scheduling by the week more than days or months, then I highly advise Week Cal. It's a colorful, concise, and simple calendar app that focuses on the weekly view. Events can be color coded based on criteria that you set to your preferences, which results in a more effective experience after set up. Week Cal supports iCloud, Google, Outlook and Exchange calendars. $2
2do: Tasks
When you need your calendar to be more than just a list of events, 2do:Tasks is an app I especially found helpful. This app is designed like a personal planner that not only allows you to add events to your calendar, but integrates your impending tasksso deadlines won't sneak up on you. If you have an iPad, this app is a two-for-one, syncing seamlessly across devices. $10 - Also available for Android
Runner Up: Fantastical
Quick mention for Fantastical, a quirky calendar app that creates events based on a small blurb. For example "Lunch, Saturday at 2pm with Susan" creates an event for the nearest Saturday for 2pm with the person and reason in the title. It's a clever little app that makes a mundane task a little more fun. $4
Android

Left: Jorte - Right: Business Calendar
Jorte
A great app for a great price (free!), Jorte is a highly customizable personal calendar app offering a great deal of options for planning/scheduling. Jorte caters more to the individual and doesn't look as daunting or sterile as common calendar apps usually do. It's quirky, fun. and advisable for people who just want to organise their lives quickly. Can't go wrong for that price either. Free
Business Calendar
Aimed at the professional user, Business Calendar is a top pick for Android users. I personally love the grandeur widget that displays either a daily, weekly, or monthly calendar on a home screen page, making it always accessible. Other than the standard event management features, what does Business Calendar offer? More frequent events can be added with ease, events can be dragged and dropped, and the multiple themes make this an app that pays for itself rather quickly in the productivity department. $5
Windows Phone

Left: Calendar[+] - Right: Beautiful Calendar
Calendar[+]
Calendar[+] is THE calendar app for your Windows Phone. It's versatile, fast, easy to add events, has room for multiple accounts, and overall feels the most solid. Events can be pinned to the home screen as a constant reminder or filter certain appointments off the calendar. Best of all, it doesn't cost a penny. Free
Beautiful Calendar
For a more robust all-in-one calendar, Beautiful Calendar offers event creation and management as well as notes and taskmaster functionality. When it comes to the calendar itself, the app's gradient UI is fashionably functional and certainly lives up to the name. The modern color scheme isn't just for looks, offering special options to mark down birthdays, anniversaries, and holidays. Free
(Image: Jason Rodway; others as linked above)

Shaw's Original Fir...
I've always used google calendar online. Now that I have my first smartphone, I wondered about calendar apps but didn't see a reason to change from the google calendar which I can share with others, etc.
Are there any pros for me to CHANGE what I am using? Anyone? The google calendar display on the phone could be better.....maybe that is the difference with an app? Sorry, as I said, I JUST got my first smartphone so I'm really not sure about all the capabilities.
Thanks!
I have an iphone and use my google calendars on the default calendar app. It took a little to get all of my calendars playing nicely with each other. I have to set up a seperate exchange server for just my google calendars to get everything to sync properly. But other than tha, I dont really have a reason to get a new app. I use paperless for my to do lists and the default reminder app for things I need notices for.
My husband and I were just discussing my inability to move to a digital calendar. I cannot find a calendar that is easier/better than pen and paper calendar. I think it might be an age thing? I have to keep track of four different schedules and cannot move digital. Did everyone start on digital calendars or did you make the switch?
We also use the google calendar on the iphone default calendar. Sharing it is ideal -- and our schools and athletic teams also use it, so it makes updates really easy.
Bittergrad - I was a staunch paper calendar person until midway through last year when I started using the google calendar on my andriod phone. It started because a lot of my bar association activities are scheduled through google calendar. And then I noticed that some online event registration systems allowed me to upload the details on google calendar automatically. it just seemed easier and I could access it from my phone and the computer. I was quickly hooked.
But, I'm only managing one (extremely busy) schedule, not four. Google calendar allows you to color-code different events - I use different colors for legal stuff, personal stuff, doctors appts, workouts, etc. Perhaps you could try using different colors for each schedule?
I miss having a paper schedule, but I like not having to lug around another book and the ease of updating or rescheduling entries.
I'm an android phone user, and with those google calendar comes with it. That's what I primarily use as well.
I used to use google calendar sync to sync my outlook to google calendar, but since google discontinued sync, I've had to maintain 2 calendars.
On Android, I use Deja Office's integrated calendar, contacts, ToDo and memos. It syncs with Outlook. I dislike putting my life on Google's Cloud.
I moved to the Google calendar and then experimented with various options. Agenda Widget+, Smooth calendar and so on. I found I wanted a daily snapshot calendar on a screen to prod me. Smooth Calendar gives me a single day look at my schedule. Agenda Widget gives me a weekly view.
I'll go check these options.
BitterGrad: I loved my paper calendar, but it got too difficult for my husband and I to stay on the same page when sharing parenting duities, e.g., he'd be setting up a follow-up doctor's appointment at the same time I'd be setting up a meeting, but we wouldn't see the conflict until we got home and put it on paper. We now use google calendar on our iphones, and it has saved a world of headache. We have five kids and the two of us are both employed and do freelance work, so having a single set of color-coded calendars that can be updated and synced in real time has been awesome. You couldn't pay me enough to go back to paper!
Calendar + for Windows Phone is indeed a must have.
I also use the Google Calendar, managing 5 different calendars. Some are managed by several people. My problem is a timezones issue. The calendar displays 2 timezones, but it screws up when I'm in NYC and scheduling an appointment in CA. Anybody has a solution, and a recommendation for another program ?
Hi, There is a New Calendar Android application, its realy productive and includes widget.
Easy Calendar
https://play.google.com/store/apps/details?id=com.dvircn.easy.calendar