I have not used this before and it is the previous version but free is still free.

DxO offers downloads of DxO ViewPoint 1 for Windows and Mac for free when you enter your email address. For comparison, the current version sells for $49. This software purports to correct complex perspectives and restore the natural proportions of volumes on the edges of photos. Deal ends February 28.

http://www.dxo.com/intl/practicalphotography