The djbwares toolset comprises these things that are not commands. See their manual pages for documentation.
caldate — calendar dates
caldate_mjd — manipulate calendar dates
caltime — calendar dates and times
caltime_tai — convert calendar dates and times
sgetopt — get option character from command line
subgetopt — get option character from command line
tai — manipulate times with 1-second precision
tai_add —
tai_less —
tai_now — get current time, with 1-second precision
tai_pack — convert TAI64 labels to external format
tai_sub —
taia — manipulate times with 1-attosecond precision
taia_add —
taia_now — get current time, with 1-attosecond precision
taia_pack — convert TAI64NA labels to external format
taia_sub —
taia_tai —
tcp-environ — UCSPI-TCP environment variables