Helios qmail is an advanced qmail distribution based on qmail-sql. It has SMTP, SMTPS, POP3, POP3S, IMAP, and IMAPS services, a content scanner, antispoof and SPF support, SMTP-AUTH, SMTP-after-POP/IMAP, a PHP5 API, and many other useful tools.
A logic analyzer, oscilloscope, and MSO GUI for sigrok.
A database engine with extreme scalability and robustness.