Elasticsearch 5.0.0-alpha3, based on Lucene 6.0.0, introduces a host of features and improvements for testing purposes as it approaches feature completeness. Notable updates include Painless scripting enhancements, indexing performance boosts, and the resolution of dots in field names to treat them as objects. The release also highlights tools like the Elasticsearch Migration Helper, which assists in transitioning from Elasticsearch 2.3.x to 5.0, and introduces the Cluster Allocation Explain API for better shard management. While this alpha version is not suitable for production, it allows users to explore changes and report issues, contributing to the development of the final release.