convcal(1) on Linux
The text c03c1de28ce2, as Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie), Debian 7 (Wheezy) shipped it.
convert dates to different formats
Flags it lists
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-h -
-i -
-o -
-r -
-w