Projity
OpenProj is an open source project management desktop application
Trello
Free tool for organizing projects. This isn't a standard project management tool, but you could use it to assign and manage tasks in a team.
Five free Microsoft Project alternatives - TechRepublic
Free options for managing projects. Some are open source. I've had mixed results with GanttProject in the past, but I may try some of these others.
Gantter - web-based project scheduling made easy
Web-based project management tool. Can import/export to MS Project. Integrated with Google Drive.
Top 10 Apps for Scheduling a Meeting Online - ReadWrite
Scheduling tools to avoid the endless email threads asking everyone what time works best
Sendtask Features
Free tool to assign tasks via email even if people don't have an account.
The PLExD Toolkit | Promethean Learning Experience Design
A collection of free and open source tools for project management, graphic design, collaboration, audio, video, and other utilities.
The 57 Best Project Management Software in 2020
An extensive list of project management software options, many of which have a free tier. Note that the list was compiled by nTask, who conveniently put their own tool on the top of the list. The feature comparisons and pricing summaries are still useful though.