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The collector is essentially a full install of Open-AudIT in ‘collector’ mode. This mode would reduce visible functionality in an effort to simplify and focus the application. It is designed to collect information about networks as opposed to focusing on the local machine (a la Agent)it's local networks and devices, where firewall and/or network traversal is an issue from the server.
Detailed information
Further details on this can be found at: Open-AudIT agent, collector, server