Spamihilator is a free, open-source anti-spam software that can be used with popular email clients such as Microsoft Outlook and Mozilla Thunderbird. It uses a Bayesian filter to learn and adapt to new spam messages, and also has a training mode for users to manually mark emails as spam or not spam. The software also includes a blacklist and whitelist feature, as well as the ability to block specific email addresses or domains. Additionally, Spamihilator can be customized with plugins to enhance its functionality.