This tool called dhtmlxGantt is a free and open source Gantt Chart made with JavaScript that helps you see the whole process of a development in charts. The tool let you visualize the dependency one task has over another, and the actual relationship among tasks. This tool has several features, among which we can count:

– Editable Gantt charts
– Integration with jQuery
– Extended control
– Drag and drop behavior
– Cross browser compatibility
– Tooltips
– Tree view
– Coloring of percentages per task
– Arrows for dependencies
– Fast rendering
– Sorting and filtering capabilities
– Custom time scale and zoom

This tool has a simple initialization, is fully customizable, its user interface is intuitive, has a rich set of features, you can export charts in PDF and PNG formats.

It has an open source – GPL license, and you can download it for free (although you can pay for a commercial or enterprise license).