TaskFreak! web based task manager / todo list written in PHP
activeCollab - open source project management and collaboration tool.
Project collaboration, management, and task software: Basecamp
Project Management, Bug Tracking, Invoicing, Leads Management, Time Tracking, and Collaboration web tools for Clever People
Doodle
Terminabstimmung online
Online Project Management Tools Web2.0 Style - Hidden Pixels
Projektmanagement mit Projectplace via Internet
Wunderkit
Trello
Instant clarity on any project Infinitely flexible. Incredibly easy to use. Trello keeps track of everything, from the big picture to the minute details.