Any free tool for Calculating Gasteiger-Hückel charges for ligands? I want to know if there is any free open source tool available for Gasteiger-Hückel charge calculation? I know it is available on Sylbyl but is there any other(free) way to calculate these charges for small molecules?

I was actually trying this paper, if any one is interested, 

How to improve docking accuracy of AutoDock4.2: a case study using different electrostatic potentials.

Hou X1, Du J, Zhang J, Du L, Fang H, Li M.X et al.
The method is not fully published according to Gasteiger.

There is an online server for PETRA run by the Gasteiger group, and in principal, it's available from Molecular Networks. I note that PETRA is no longer listed on the products page, but it's probably part of some other product now.

The open source CDK package has an implementation of the PEPE method, although I don't know if it has been validated against Gasteiger's code.