[allannienhuis]

not open source (and not the above calendar), but similar and useful if you're not on windows: https://docs.google.com/spreadsheets/u/2/d/1m1IWh6Mmli8K20Dd...

[+ attribution] Many thanks to Pedro Pablo Fuentes Schuster for this Google Sheets conversion! http://pedrofuent.es/

[j1elo]

Nice, thanks!