http://www.openoid.net/products/
https://github.com/jimsalterjrs/sanoid
Features
Rolling hourly snapshots
Policy driven management.
Monitoring
Nagios.
Asynchronous Incremental Replication
Rapid disaster recovery.
Hardware decoupling
Easy upgrades, don't need spares for exact replacements.
Building blocks
KVM
Built into Linux kernel.
Fast.
Virtmanager
Single instance can manage VMs on multiple hosts, using ssh.
OpenZFS
Handles snapshots and block-level replication.