PGP
www.pgp.com

Magic Money Digital Cash Systems
www.c2.org/~mark/pgp/mm-readme.html

Digicash
www.digicash.com

First Virtual
www.fv.com

Cybercash
www.cybercash.com

Open Market
www.openmarket.com/products

Secure Electronic Transactions
www.rsasecurity.com/rsalabs/faq/4-2-3.html

NetCheque
gost.isi.edu/info/NetCheque

NetBill
www.ini.cmu.edu/netbill