start.me - A Modern-day bookmark manager. A place for your favorites. A news feed (RSS) reader. A browser startpage. A portal for your team.
LibHunt - LibHunt tracks mentions of software libraries on relevant social networks. Based on that data, you can find the most popular projects and their alternatives.
Netvibes - First personalized dashboard publishing platform for the Web. Digital life managment, Widget distribution services and brand observation rooms.
AlternativeTo - AlternativeTo lets you find apps and software for Windows, Mac, Linux, iPhone, iPad, Android, Android Tablets, Web Apps, Online, Windows Tablets and more by recommending alternatives to apps you already know.
Protopage - The best iGoogle alternative. Chris Pirillo calls Protopage "The best designed".
JSter - JSter is a community-driven catalog of the most useful javascript libraries.