SharePoint 2013 - SharePoint Apps

SharePoint Apps Features Overview

The Apps are here! SharePoint 2013 brings a new approach to Sandboxed Solutions as they’ve been replaced in SharePoint 2013 with "SharePoint Apps".

SharePoint apps have more powerful capabilities than Sandboxed Solutions such as the ability to utilize cross site collection data, have unique locked down permissions, and are built with familiar languages and IDE's. SharePoint Developers are already digging in and creating custom apps to improve their solutions and benefit others.

Some facts about SharePoint 2013 Apps:

The App doesn't affect the SharePoint farm performance (though may flood the farm with client side object model calls)
Developers can package and distribute their SharePoint Apps on the new Microsoft App store which works with On-premises SharePoint, Hosted SharePoint (Fpweb.net), or the Microsoft Cloud (Office 365)

SharePoint Apps can be hosted in an isolated SharePoint Site, isolated server, or even on Windows Azure
Server side code is not possible for Apps (farm solutions are required here)
SharePoint Apps rely on OAuth 2.0