The next frequent way of organizing after plain text, is to stuff everything into one monolithic application - an e-mail client, or an outliner, or whatever.

The Evolution mail client provides the same functions as Microsoft Outlook, including multiple E-mail accounts, contacts, calendars, tasks, and memos integrated into a single application.

This demo app is a simple mail client, utilizing jQuery to give users the feeling of working with an E-mail client that is actually a desktop application.