The Carnival of Mathematics is a monthly blogging round up hosted by a different blog each month. It is run by the Aperiodical and can be found here: https://aperiodical.com/carnival-of-mathematics/
The Carnival of Mathematics accepts any mathematics-related blog posts, YouTube videos or other online content posted during the month: explanations of serious mathematics, puzzles, writing about mathematics education, mathematical anecdotes, refutations of bad mathematics, applications, reviews, etc. Sufficiently mathematised portions of other disciplines are also acceptable.
In the Carnivals thus far, I have been in the:
April 2020 Carnival: