Mirroring data between clusters
We have a tool that runs a continuous copy between two clusters. The clusters are completely independent and the topology need not match (you can have a different number of brokers and a different number of partitions). Offsets and partitioning are currently not preserved by this tool as it is meant for geographical replication rather than backup.
Documentation here.
Administrative tools
A set of tools for managing an 0.8 cluster is described in here.