Office is the old classic that you are familiar with but with a web based kicker...
Exchange and Outlook were built for maximum compatibility offering features when used together that you can't get when used separately.
Exchange is awesome but its not cheap!
Conservative cost approximation for a small business with 20 users
Conservative cost approximation for managed I.T. services ex. software version upgrades
Subscription costs for a small business with 20 users on Office 365 Small Business Premium
Automatically sync all of your files back and forth between computers and mobile devices with OneDrive for Business installed.
Making a change to one of these documents within OneDrive on a device (Desktop, Laptop or Mobile) will be synchronized across all linked devices and your Microsoft Office 365 Cloud Storage within SharePoint.
Work seamlessly together with colleagues and contractors to provide the the most productive and efficient outcomes on PCs, laptops and mobile devices...
With the Office 365 service it’s Microsofts responsibility to keep your data safe and secure. It’s your data. You own it. You control it. And it is yours to take with you if you decide to leave the service...
Office 365 requires Windows 7 or 8. Mac users need OS X 10.6 (or later). You'll also need Internet access to install Office 365 and to activate and manage your subscription (once a month). You'll need a compatible browser. IE 9, Firefox 12, Safari 5, or Chrome 18. Regarding hardware, at the very least, your local system will need the following.
Users with older systems may face significant upgrade costs to move to Office 365.
Office 365 runs offline. You must connect to the internet every 30 days to maintain your subscription. Office 365 will let you know when it's time to connect.