You can integrate vCenter and Free/TrueNAS for snapshot quiescence; there's no software; just a logon @ vCenter needed and it's managed under VMWare Snapshots under Free/TrueNAS
Then if you schedule a LUN for snapshots within Free/TrueNAS then it will API to vCenter to have the machines all take a snapshot; then the LUN snaps, then the snapshots are released.