Lee Meredith's relatively new coloring book, Color Squared: Color, Dot, Dash, or Stamp Your Way to Awesome Pixel Art, riffs on the idea of paint-by-number by showcasing pixelated images of cool and quirky nostalgia objects — cassette tapes, a rotary phone, rollerskates, a vinyl record player, a Rubik's cube, etc.
As the name implies, you don't have to completely fill each "pixel"; you can fill them with circles, lines (in various orientations and combinations), hashtags, starbursts/asterisks, gradients (if you're feeling fancy), or whatever other patterns you like. Whatever you choose, it's all a great way to relieve stress and/or challenge the part of your brain that loves puzzles.
Get it for $11 on Amazon.