Even if there was a FLOSS option that checked every box on features, there would still need be an RFP for implementation. You can't create and manage the infrastructure of a system at that scale without spending enough money to require an RFP.
Always fun to get downvoted for voicing a statement of fact: an RFP is required, if I remember correctly, for any purchase in excess of $25,000. It's not a high bar, and would easily be surpassed by having to pay a contractor to implement and integrate even the simplest of tools if it's to be used across the entire DoD Enterprise.
