I'd love to say that the most interesting thing here is Fly Machines (i am bias) but really it's SQLite, which, no matter what platform you're using, makes it architecturally simpler to scale up and down, since you don't have to scale a database server up and down with your workload; the database is embedded in the app, which already had the scaling logic.

People have been sleeping on SQLite and are starting to wake up and I'm kind of psyched to see what else they come up with (another very cool example of a software tool that really plays to SQLite's strengths is Datasette: https://datasette.io/).