I represent team of developers-enthusiasts, who created Web-based project management tool LetsPlanIT-Web. We did it for our own needs and projects. Two years of internal usage proved implemented concept. So we decided to make it public. Please check details about the product on http://www.letsplanit.org/
The main difference of LetsPlanIT-Web from the most PM tools available on the marker is possibility to balance loading of resources between several projects running simultaneously. Another advantage is in possibility to make project status clear for the customers. It is free of charge and does not require any installation on the client side (AJAX-based light client with rich GUI).