Hypertable is an open source, massively scalable database modeled after Google's Bigtable. It is written in C++ for high performance and supports Apache Thrift interfaces for popular languages. Hypertable is actively developed, has over 8 years of development, and supports features like namespaces, atomic counters, secondary indexes, regex filtering, and Hadoop integration. It is designed for horizontal scalability and sparse data structures, allowing for high throughput on both reads and writes even with large datasets.