Loads of Topics on my mind.
1. Shared Multi-Stack Cross-App Platform-Independent Clipboard
2. ChatToday - Web based Chat App with Q&A + Poll,
Inbuilt Location and Time Tracking, built on PHP and MySQL DB. Use GPS if possible, else (reverse) IP-lookup
3. WebHyperLinksToday - Users get a mail with a screenshot of a website's homepage daily with an iframe version of a new random website depending on user's perferences, fields of interest and search keywords.

4. ScreenshotsToday - Registered Users can Upload Screenshots to a Global Gallery. or Add to their own private/public Collection. People can view Galleries by OS/Browser/Content-Keywords/Username
5. PollToday - Daily Poll based on high-frequency keywords used by users