Any commercial or open-source public key encryption tool? I have been using GPG4Win from quite some time and looking for any alternative.
Difficult to answer your question. GPG4Win is a Windows front-end for GnuPG, which is the actual command line based encryption application. Are you leaving because you don't like GnuPG, or you don't like the front-end? GnuPG is pretty much the gold standard public - private keypair encryption app. It can handle files, text, and as an add-on to email applications (like Thunderbird) can encrypt and decrypt email messages. GPG4Win is a clunky, heavy GUI, and development moves ahead really slowly, probably because the user base isn't very large. I am not aware of any open source key pair alternatives to GnuPG. PGP (not free) might still be out there. Last time I checked it was owned by Symantec.