Madvent Calendar 2021 is a collection of short game vignettes from members of the HPS1 community. There are 25 games available from a launcher, one for each day from December 1st through the 25th; these games are not demos, so there is no further development for these titles unless specified otherwise. Unlike the first Madvent Calendar, the games in this launcher are not locked behind an advent system that would unlock the games when their specific day is reached, except for the final game.