If you want something easy and free I suggest Trello. https://Trello.com
Plus they are owned by Atlassian who make Jira.
Apart from Gantt charts, you can use Tasks lists and Network diagrams.
These three tools can help you a lot. Apart from that, one more tool I would like to mention is Kanban cards. We use them at Apps4Rent where I work.
And we have improved drastically by using these tools.