The puzzle above is the Science Lab pack — on the workbench. It draws on a list of 58 science words, and every level deals a fresh grid from that list, so the pack does not run out after a handful of puzzles. No timer, no signup, nothing to install.
Every word below can turn up in a grid:
The largest grids, with words running in every direction including backwards. Worth saving until you have the scanning habit.
Drag across the letters to mark a word — press on the first letter and release on the last. Words can run left to right, top to bottom, diagonally, and backwards. Found words are struck through in the list, and your progress on a grid is saved as you go, so you can stop mid-puzzle and pick it up later.