Both giver and recipient are unknown to each other, mediated through a trustworthy third party. The Rambam's example: the Temple chamber of secrets.
The Third Level: Full Anonymity
Level three of the Rambam's eight levels is: "One who contributes without knowing the recipient, and the recipient takes without knowing the identity of the giver." Both parties are unknown to each other. The Rambam's historical example is striking: the lishkat chassidim — the Chamber of the Discreet in the Temple.
The Lishkat Chassidim
In the Temple period, there was a special chamber where wealthy people would deposit money quietly, without fanfare. Poor people, equally without announcement, could enter and take what they needed. No one knew who gave, and no one knew who took. The entire economy of the exchange was structured to preserve dignity on both sides.