FoundationDB is a NoSQL, YesACID scalable layered database that worked faster and needed less hardware than other services of its kind. FoundationDB core was private but it offered several tools as open source that many developers operated with and relied upon. In 2013, FoundationDB had released a paid and community version available for download.
Apple acquired FoundationDB in 2015, presumably to replace the noSQL it was using (Cassandra) or to integrate it into some of its cloud services. When the acquisition took place, FoundationDB was made to remove its downloadable software from the website. Also, its open source components became unavailable to the public. This caused a great deal of distress to the developer's sphere since many were using FoundationDB tools to run live companies and not only for research purposes.