Google Apps provides a set of collaboration, file sharing, and productivity tools, including:
<!--[if !supportLists]-->· <!--[endif]-->document authoring
<!--[if !supportLists]-->· <!--[endif]-->calendaring
<!--[if !supportLists]-->· <!--[endif]-->spreadsheets
<!--[if !supportLists]-->· <!--[endif]-->email
For a variety of reasons (such as cost, privacy, control) you may prefer to “roll your own” productivity suite, which you would host on your own server — whether on hardware you own and maintain yourself, colocated hardware, or VPS hosting plan.
Currently, the best all-in-one option for building this kind of collaboration system is the Open Source ownCloud project.