SDF Public Access UNIX System

A public-access UNIX system, run as a non-profit, offering shell accounts, personal pages and mail on shared machines — the arrangement most hosting grew out of, still operating.

A stub, and possibly out of scope rather than listed. Membership is a donation to an association rather than a plan bought at a price, which is the question to settle before this appears in the register: whether it is sold to the public in the sense criterion 2 means.