SharePoint online has many features that we have not discussed. Some of these might interest you but would require entire books to explain. This chapter has focused on features and capabilities that you can implement without custom code or specialized technical skills, such as designing a database. However, you can write custom applications for SharePoint Online by using sandboxed solutions. This gives you tremendous flexibility to provide specific features—such as custom workflows, integrated mobile applications, forms processing, and other line-of-business integrations—that go beyond what you can create using pre-built Web Parts. These applications are referred to as sandboxed because they have some limitations enforced by the host environment. In other words, Microsoft limits the scope of custom SharePoint Online applications so that they do not risk the performance and availability of the service.