- archiver format to stow multiple files in one; your actual files (in your choice of format(s)) go inside

- files can be individually extracted, in any order, from the archive

- thousands of implementations available, in every language and every architecture. no more than 32KiB RAM needed for decompression

- absolutely no possibility of patent challenges

Also architecturally suitable for the common case of collecting heterogeneous files in existing and new formats into a single file, as opposed to designing a database schema or a complex container structure from scratch.

Any multi-file archive format would do, but ZIP is very portable and random access.