The MIT puzzle (from the 2013 Mystery Hunt) was called "A Regular Crossword" and its credit says "Dan Gulotta, based on an idea by Palmer Mebane".

(Just so it's not credited to MIT in general; each year's Mystery Hunt is written by a specific puzzle team, and indeed each puzzle is written by specific puzzlers!)

This new site is super-awesome and challenging, but a great thing about the hexagonal grid in "A Regular Crossword" was that each hexagon was constrained by three intersecting regular expressions rather than two. That meant that the constraints could be trickier or vaguer in some ways, and comparatively more dependent on the sequence of elements within a regular expression rather than on the process of elimination between two intersecting sets.

Elsewhere in this thread, a commenter points out that the square grid regular expression puzzle can encode 3SAT instances, so I was wrong to call these easier than the hexagonal version.

I liked this puzzle too and I also made a web based version: http://stardrifter.org/regexp/ . Yours looks nicer but I do miss one feature from my version which is the ability to click a clue to rotate it into view.

Thanks, that was fun and not as tricky as the blank grid initially made it appear! And the implementation was nice (although a little twitchy if you rotate twice quickly).