I am interested in knowing the lipinski parameters and TPSA/PSA for my molecules. Can anyone suggest me a reliable tool ( free downloadable version) for it?
There are a number of open source or other tools available to achieve your aim here.
The RDKit API (http://www.rdkit.org/) allows you to calculate TPSA using the model published by Peter Ertl et al. (http://www.peter-ertl.com/reprints/Ertl-JMC-43-3714-2000.pdf), however this might require some simple scripting, but using the myChEMBL distribution that includes RDKit already installed (http://chembl.blogspot.co.uk/2013/10/chembl-virtual-machine-aka-mychembl.html).
You can also use the online tools from MolInspiration (http://www.molinspiration.com/cgi-bin/properties) to calculate this property, but you might not like to send your structures out over the Internet unencrypted and to an external server.
My last suggestion would be to use DataWarrior (http://www.openmolecules.org/datawarrior/), a free data visualisation tool for drug discovery that allows for the calculation and interrogation of a number of molecular properties directly inside the application. For ease-of-use, I would recommend this option for most purposes, and the software also offers a great deal of additional features and functionality.
There are lots of tools out there to answer your question, but these would be my first places to start. Hope this helps, Nath.