The future of operating systems and applications is online, everybody knows that, it's not exactly a secret. Google are leading the way into this new frontier with their web applications such as Google Docs (word processor and spreadsheet), Picasa web albums (photos) and Notebook (collaborative note taking), to name a few of the ones I use. Technologies like AJAX are making it possible to create a similar user experience in an online application as an offline application. Perhaps in the future Flash will also be used to create applications - it's certainly what Adobe would like.
The future isn't just online though, the future is also offline.