@julia you can operate on atproto without any involvement with bluesky at all! it's just that bluesky, being the killer app, has become ubiquitous among atproto identities.
anything definable in atproto's lexicon format is saveable in an atproto PDS, including blobs
i could build an entire identity off only ever using flushes.app and that would be totally valid
i love federated software architectures