Archiver supports the following formats out of the box.
The zip-stream package is used to produce ZIP archives.
The tar-stream package is used to produce TAR archives.
GZIP compression is also suppported.
The JSON format is designed primarily for debugging and just collects and stringifys the entry data into JSON.
Archiver also supports the registration of custom archive formats.
The API for this is rather simple at this point but may change over time.