Users enter their problem reports (PRs) via some front-end. This front-end either directly contacts the gnats server, or sends the report via e-mail. (The server is available since about version 3.90 of gnats). For an incomplete list of front-ends see Clients.
Some front-ends (like TkGnats, see TkGnats) are capable of contacting several gnats servers, or several problem report databases managed by the same gnats server.