This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Pardon me for being clueless, but I don't see what a CMS has to do with implementing a form builder.
One would think a Google search could turn up a number of open source CMS products.
Perhaps if you gave us some of your specific requirements (TellTheDetails) we may be able to give you some help.