Third Party Software for SpamAssassin

Web UIs for administration or per-user configuration: WebUserInterfaces
Commercial SpamAssassin products: CommercialProducts
Statistics and analyzers: StatsAndAnalyzers
Firewall/Passthrough like filter: OpenProtect, AssassinDeamon, [http://www.etc.msys.ch/software/smtp-vilter/index_html/view SMTP-vilter]
Central integration of sa-learn with IMAP shared folders: RemoteImapFolder
Free Open Source Windows POP3 proxy (unsupported): SAproxy (but not SAproxy Pro)
Let users run SpamAssassin on messages during the SMTP session: [http://www.mailavenger.org/ Mail Avenger]

ThirdPartySoftware