Linkage

The EFF on FLoC ($\mathbb{M}$), Google’s plan for browsers to aggregate your browsing habits and make them public for ad-personalization. Short summary: it’s a bad idea and if you care about privacy you should switch to a non-Chrome browser. Technical summary: it’s based on k-anonymity, known as inadequate at protecting individual privacy in social networks. If you use Chrome, assume all bad guys on the web can see all your browsing.
Relevant to my recent post on Pick’s theorem: Chris Staecker on the dot planimeter ($\mathbb{M}$), a device for approximating area by counting grid points.
Anamorphic street art by Peeta transforms building shapes into 3d geometric abstractions ($\mathbb{M}$, via).
Students of University of Minnesota assistant professor Kangjie Lu caught allegedly deliberately sending buggy patches to Linux kernel as some kind of breaching experiment, resulting in the whole university being banned from Linux kernel development ($\mathbb{M}$, via). They claim to have been declared IRB-exempt but this appears to be a mistake by the IRB. See also department reaction and metafilter discussion.
Josh Millard plays with algorithmically-generated pen-plotter art; more.
You could prove that the number of integer solutions to $x^2+xy+y^2=a$ is a multiple of six for positive $a$ by finding a hidden group structure ($\mathbb{M}$). Or, you could recognize that it’s the norm of the Eisenstein integers under a small change of basis from the usual one and that they have six-fold rotational symmetry.
Paper engineering from the Bauhaus and reverse-engineering Bauhaus paper designs ($\mathbb{M}$). These designs are more curved kirigami than origami, producing smooth-looking 3d shapes from cut sheets of flat paper.
The art of mathematics in chalk ($\mathbb{M}$, see also). Teaser for the forthcoming book Do Not Erase: Mathematicians and Their Chalkboards, featuring several photographic spreads of chalkboard illustrations and formulas and their explanations. They appear to be mostly set-ups rather than captured from active research, but still pretty and interesting. I linked an earlier post on this in 2019 but with fewer photos and no explanations.
The Coq theorem prover brainstorms a name change ($\mathbb{M}$, via), after too many women get harrassed for saying they work on Coq.
Tetrad puzzle ($\mathbb{M}$). It’s possible to arrange four congruent hexagons so they tile a disk with each pair sharing a length of boundary, but the known pentagons with four pairwise-touching copies leave a hole in the region they tile. Is the hole necessary?
Mercator Rotator ($\mathbb{M}$), a tool for drawing Mercator-projection world maps with different viewpoints than the usual one. Set the pole on a place you don’t like to see the map of a world without it.
Tetrahedra passing through a hole ($\mathbb{M}$). This is from eight years ago, but was active again recently. The question is: what’s the smallest-area hole in a plane through which you can push a unit tetrahedron? DPKR has a very pretty animated answer, but sadly it’s not optimal: there’s a triangular hole with smaller area $1/\sqrt{8}$, known minimal for translational motion. The problem for more general motion seems to be still open.
Lagarias’s survey on the Takagi Function and Mallows’ survey on Conway’s $10,000 sequence ($\mathbb{M}$, via, see also) have very similar-looking figures, but little or no overlap in references. Maybe someone knows of an explanation for the similarity?