CVS's password-authenticating server — version control from before SSH was assumed.
The CVS manual documents 2401 as the default pserver port, historically wired up through inetd or xinetd running cvs pserver. A client sends the repository root, username, and password, and gets read/write access to the repository. The manual is blunt about the security: the password is only trivially scrambled, offering no protection against anyone who can sniff packets, and it recommends a separate CVS password file so people do not expose their real account passwords. Today it turns up on legacy source servers and anonymous read-only mirrors of old projects.
Do not expose
The CVS manual itself says the scrambling stops inadvertent compromise and nothing more; authenticated pserver on a public IP hands over credentials. Anonymous read-only mirrors are the only defensible case, and even then prefer ssh transport.
$ nc -v TARGET 2401Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.