CasBase is an open source project that aims to add secondary indexing capabilities to Apache Cassandra similar to relational databases by implementing techniques like composite columns, hashed and ordered buckets for indexing, and custom data types to support null values. The presentation discusses the motivation for CasBase, how it implements various indexing approaches like unique and non-unique indexes, and deals with challenges of Cassandra's data model like null values. CasBase is available on GitHub and provides a concrete way to build indexes in Cassandra through its API.