Foundation is fundamental to iCloud at Apple, and is _something_ at Snowflake, among a few others. Recently DeepSeek used it for https://github.com/deepseek-ai/3FS "The Fire-Flyer File System (3FS) is a high-performance distributed file system designed to address the challenges of AI training and inference workloads."

I don't think that there's anything else quite the same, partly because it has some real oddities that manifest because of things like the transaction time limits. At Apple they worked around some of this with https://www.foundationdb.org/files/QuiCK.pdf