Apache Calcite is a modular framework useful for building query processing and optimization systems over heterogeneous data sources. You can view a preprint of a paper describing more of the details of Calcite on arXiv. I am currently serving as the project management committee (PMC) chair.
NoSE is an automated schema design tool for NoSQL databases.
Locomotor is an exploration of the automated translation of application code accessing a database into stored procedures.
NetStore attempts to utilize software-defined networking to improve the performance of key-value stores.
FlurryDB is a dynamically scalable relational database which makes use of virtual machine cloning.