It's a implementation of "TCP Based Daytime Service" Daytime Protocol [RFC867]. It replies with a Japanese pronunciation of the server's local time.
Collaborator: @kory33
Note
For machine useful time use the Time Protocol (RFC-868) yanorei32/timed-rs.
./nichijid-rs # default port usage (0.0.0.0:13)
./nichijid-rs 0.0.0.0:1313 # specific port usage
NOTE: 13 is a well-known port. It may require administrative permission.
$ nc localhost 13
ni-sen ni-juu san nen hachi gatsu juu hachi nichi kin youbi juu ji roppun juu san byou