A few programs:
- Tor: “enabling Internet anonymity by thwarting network traffic analysis”
- Privoxy: “It has filtering capabilities for protecting privacy, modifying web page data, managing cookies, controlling access, and selectively removing content such as ads, banners and pop-ups.”
- Enigmail: “It enables you to write and receive email messages signed and/or encrypted with the OpenPGP standard.”
- Off-the-Record Messaging (OTR): “cryptographic protocol that provides strong encryption for instant messaging conversations”
An interesting talk on Youtube: