For time-strapped entrepreneurs, managing an ever-growing calendar full of deadlines, appointments and tasks can be a headache. It might not take much to fall behind schedule or miss an important meeting. Luckily, apps that help remind us of events and engagements can come in handy, and help keep us productive.

If you're tired of being late or veering off task, try one of these apps to help you stay on-task and on-time:

1. Any.do
This free app organizes your appointments and to-dos into a single, swipe-able list that's easy to use. Tap the microphone icon to enter new tasks and meetings to your list with your voice. Drag and drop individual to-dos to prioritize, share and add reminders to them. Simply swipe a task to mark it as complete. To clear completed items, shake your device. 

Any.do is available for Android, iPod touch, and iPad.

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2. Toodledo
Toodledo is an all-in-one taskmaster that helps you take control of your schedule, organize tasks and be more productive. The $2.99 fully-featured version comes with customizable task and appointment lists that seamlessly integrate with your email and calendar.

Stay focused on upcoming important tasks and meetings by filtering them by priority, context, tags and subtasks. Reduce the chances of being late to a meeting or missing a deadline with Toodledo's reminder alarm feature, which lets you schedule reminders to arrive via email, text message or over Twitter.

Toodledo is available for Android, BlackBerry, iPhone, iPod touch and iPad.

3. Leave Now
This free app keeps you on time for your next meeting by telling you exactly when to leave. It posts a reminder message on your iOS device's (iPhone, iPod touch and iPad) home screen precisely when it's time to get up and go.

Using GPS, LeaveNow automatically calculates traffic for various modes of transportation, including walking, biking, driving and public transportation, and adjusts your departure times and reminders accordingly. When you're running late, Leave Now sends "on my way" texts and emails on your behalf to let people know your estimated time of arrival -- all in a single tap.

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4. CalAlarm
For $1.99, CalAlarm offers a no-frills, user-friendly calendar app that helps keep you on-task and on-time by sounding motivating reminder alarms. Easily create, snooze and repeat multiple alarms per event. Alarms can be set to recur on a per-minute, hourly, daily, weekly or monthly basis.

Stay focused with 25 CalAlarm sounds (tropical organ, drumbeat, bell and more). Available for iPhone, iPod touch and iPad, those running iOS 5 or later can customize alarms using iTunes ringtones or songs stored locally on their device. CalAlarm syncs with iCal, iCloud, Microsoft Exchange, Microsoft Outlook and Google Calendar.

What tools do you use to keep you on schedule? Let us know in the comments below.