The "sha3sum" command:

Usage: fossil sha3sum FILE...

Compute an SHA3 checksum of all files named on the command-line.
If a file is named "-" then take its content from standard input.

To be clear:  The official NIST FIPS-202 implementation of SHA3
with the added 01 padding is used, not the original Keccak submission.

Options:

   --224        Compute a SHA3-224 hash
   --256        Compute a SHA3-256 hash (the default)
   --384        Compute a SHA3-384 hash
   --512        Compute a SHA3-512 hash
   --size N     An N-bit hash.  N must be a multiple of 32 between 128
                and 512.