cover the whole grid by drawing a single line through numbers in ascending order. 150 levels after the tutorials, conveniently all available from the start, with grids between 6x6 and 20x20. there's a random level generator as well.

numbers have to be connected one after another mathematically, but you can do 7-8 or even 8-7 first if you want, then 3-4-5 (or 5-4-3), etc. until it all makes sense. letting go of the mouse before reaching the next number cancels the line between the last two numbers, as does right click on any connection. while the mouse is held, you can go back on your selection and take another direction.

controls are mouse-based with some hotkeys revealed on mouseover. unfortunately, it's another title mistaking a game with microsoft office and such, so reset is the cumbersome ctrl+r combo and undo is ctrl+z, while esc asks if you want to quit the level. I wouldn't mind lines not disappearing if the next number is not reached, just stopping where I let go, and an alternate click-click method on top of the holding one for accessibility. and level select should jump to the first unsolved level, not always the top.

functional presentation, unintrusive audio, resolution options, windowed mode, separate volumes (master and music), vsync toggle, and dark mode got patched in quickly upon request. settings are only available from the main menu though.

decent draw a line puzzlers are surprisingly rare on steam but this would be a good one (later/bigger levels offer more of a challenge), except mid-level progress is not saved. didn't get any of the achievements either but I don't care about that and they seem to work for others.