From their Wikipedia entry:

Thawte Consulting is a certificate authority (CA) for X.509 certificates. Thawte, (pronounced like "thought"), was founded in 1995 by Mark Shuttleworth in South Africa and is the second largest public CA on the Internet.

Thawte offers free email certificates that can be used sign Java code for use in Java Applets (Richard Dallaway's Java Web Start and Code Signing page provides the details on how this can be done).