PNotes is light-weight, flexible, skinnable manager of virtual notes on your desktop. It supports multiple languages, individual note's settings, transparency and scheduling. Absolutely portable as well - no traces in registry. PNotes.NET edition requires .NET framework 4 Client Profile
Free flexible open source todo manager featuring hierarchical tasks
Task Coach - Your friendly task manager. Task Coach is a free open source todo manager. It grew out of frustration about other programs not handling composite tasks well. In addition to flexible composite tasks, Task Coach has grown to include prerequisites, prioritizing, effort tracking, category tags, budgets, notes, and many other features. However, users are not forced to use all these features; Task Coach can be as simple or complex as you need it to be. Task Coach is available for Windows, Mac OS X, and GNU/Linux; and there is a companion iOS app.
Collabtive is web based project management software. Simple and easy.
Collabtive is web based collaboration software. It is an Open Source alternative for proprietary tools like Active Collab or Basecamp. Features include: Projects, Instant Messenger, Tasks, Files, Timetracking, Multilanguage, Basecamp import
A web-based project management tool for workgroups. Encourage groups and individuals to work collaboratively. This tool aims to be functional and elegant without being complicated or graphically intensive.
Simple Online Planning
SO Planning is a Simple Online Planning tool. Allows you to plan working periods for each person of your team, in a visual / printable result. Shows a line by person and the corresponding working days. See http://www.soplanning.org for details.
ackerTodo is a web-based todo list manager which supports multiple users, recurring tasks, multiple languages, categories and much more! It's written in PHP/MySQL.
Rachota is a portable application for timetracking different projects. It runs on Windows, Linux, Solaris and Mac. It displays time data in diagram form, creates customized reports or invoices and provides suggestions to increase your effeciency.
IGSuite is a web-ajax-based Integrated Groupware Suite
IGSuite is a web-based Integrated Groupware Suite oriented to be a CRM solution. In the Suite you can find: IGWebMail, IGCalendar, IGContacts, IGArchive, IGWiki, IGTodo, IGChat, Projects, IGFax an HylaFax client, IGFileManager, IGMsg and many other.
RemoteCalendars is a COM-.NET Add-in for Outlook 2003/2007, written in C#. After installing this plugin, every Outlook user should be able to subscribe, reload and delete a generic remote iCalendar (RFC 2445) from Outlook 2003/2007.
Teamwork is an integrated, web based work management solution built purely in Java on the Hibernate persistence layer. It integrates project, time and worklog management. Import/export from MS-Project, Basecamp and Outlook/Icalendar SVN & Tweet synch.