It is possible to create Gantt charts on the wiki using an XML based project plan description. Instructions are here: http://www.logilab.org/projects/pygantt/documentation and http://moinmoin.wikiwikiweb.de/ParserMarket/Gantt
Note: I've removed this feature for now, since it is extremely difficult to use. You have to painstakingly edit an XML file to create the chart and there is no GUI.
<project xmlns:pg="http://www.logilab.org/namespaces/pygantt_docbook" id="monprojet">
<label>Cytoscape</label>
<task id="module">
<label>Testing</label>
<task id="func1">
<label>Code Freeze</label>
<duration unit="days">1</duration>
<constraint type="begin-after-date">2005/08/15</constraint>
</task>
<task id="func2">
<label>Testing</label>
<duration unit="weeks">4</duration>
<constraint type="begin-after-date">2005/08/15</constraint>
</task>
</task>
</project>