Biased opinion here (Aerospike CTO and Founder), but you might want to check out open-source Aerospike DB. Like Foundation, it's clustered by default, very very good at SSD / Flash, runs great in cloud deployments, etc.
It's been used in production by big ad houses like AppNexus as well as retailers like SnapDeal. Lots of miles on the code.
Was closed source for years, but went open source about 9 months ago.
No high availability on open-source. Meant to be used with partitioning in mind so if you need cross-partition transactions most of the time, it's slow.
VoltDB has fantastic HA, but yes, not in the OSS version.
You might be surprised how many apps deploy on VoltDB with cross-partition transactions making up a solid chunk of their workload. Yes, they're slower than partitioned operations, but they're still faster than MySQL much of the time.
Most of the apps we see partition very well, especially for writes. The fact that they can run 10k distributed aggregates a second to get a global view is something few other systems can touch.
It's been used in production by big ad houses like AppNexus as well as retailers like SnapDeal. Lots of miles on the code.
Was closed source for years, but went open source about 9 months ago.