JECmate is an application to help manage chess games played by mail or email. Written in Java it will support the creation of messages and the sending of those messages by email. It may also be used as an interface to third-party chess engines.
jmailto is a tiny JavaApplet which can be used to replace HTML's native "mailto:" tag. It aims to prevent Spam bots and harvesters from automatically collect (your) E-Mail addresses by searching the HTML source code of your page.
SWM (Secure WebMail) is an applet that provides confidentiallity and authentication in webmail applications using SHA/RSA algorithms. It can accompany virtually every webmail application, but comes with a plugin for squirrelmail and can run standalone.