Develop Cloud-Based Collaborative Solutions with SharePoint Online and Office365 Beta

In addition to Office Professional 2010, the Office365 Beta includes an
updated communication and collaboration suite known as Microsoft Online
Services. It consists of the cloud-based versions of Exchange 2010, Lync
Server 2010, and SharePoint 2010.

The process of building solutions for SharePoint Online is similar to
SharePoint 2010. Developers can use the same tools they're accustomed to,
such as SharePoint Designer 2010, Visual Studio, and the SharePoint API and
SDKs. However, there are several key differences that must be taken into
account when planning to deploy a SharePoint solution on Office365 Beta.

For example, Farm scope (for an entire server farm) is not available on
SharePoint Online, as it runs in a shared datacenter with multiple clients.
Only Site and Web scopes apply in the cloud. Full Trust is not available for
the same reason.

While a majority of SharePoint 2010's features are also available for
SharePoint Online, some are not supported. (The Office365 documentation
provides a full side-by-side comparison of the two platforms.) Business
Connectivity Services are not currently included, but there are plans to add
them at a later date. One of the more interesting exclusions from SharePoint
Online is Web Services, because their use is not supported in only
partial-trust applications. Microsoft does note, however:

"Although … external data connections are not available for use in
sandboxed solutions, you can access them through client applications such as
Microsoft Silverlight and ECMAScript (JavaScript, JScript)."
Because of the limitations of using SharePoint Online in the cloud,
Microsoft recommends developing for it using Sandbox Solutions, so that
applications will automatically meet the criteria for scope and trust.

Sandboxed SharePoint solutions in Visual Studio 2010 support IntelliSense,
but do not include compilation support. To aid with this, Microsoft recently
introduced Visual Studio 2010 SharePoint Power Tools, which add compilation
support and a Visual Web Part project item template specifically tailored to
sandboxed SharePoint Online projects.
The SharePoint Online developer guide is available now from the Microsoft
Download Center.