Simply gently ganttly!
ganttly is gantt chart editor utilizing dhtmlxgantt.
ganttly is just single static page. You can try it just opening index.html locally.
$ git clone https://github.com/swcho/ganttly.git
$ cd ganttly; chromium-browser --disable-web-security index.html
Or, you can just deploy it under any web server directory.
In some case, you should disable browser security to avoid CORS error. For example, you should launch chrome with next command and option.
$ chromium-browser --disable-web-security
You can try codeBeamer with JavaForge. You need to create account in [JavaForge] and make some project with tasks. Then you can tryout with next URL. http://swcho.github.io/ganttly
If you have trello account, try to open next link. http://swcho.github.io/ganttly/#/ganttTrello