One studio, a short list of apps
The registered company is AK Kajtna d.o.o., at Ljubljanska cesta 2, 1270 Litija, and Igor Kajtna answers for what it publishes. DEV is the name on the software.
Apps are designed, drawn, written and released here, one at a time, and then kept in repair instead of being abandoned for the next idea.
The constraint everything follows from
An app should do its whole job on the device. That one decision removes the account, the sign-in, the sync, the analytics pipeline and the advertising that usually pays for them — and with them most of the ways an app can go wrong.
Nothing is wired to anything
What an app needs to remember goes into its own private folder on the handset, which Android keeps sealed off from every other app installed. No identifier is minted, no event is counted, and no advertising library is compiled into the build.
There is no database here to lose, nothing to hand on, and nothing that stops working the day a service is switched off. The trade is that progress lives on the phone and nowhere else, which is worth knowing before a handset is replaced rather than after.
Tok
Connect · Flow · Fill the void
com.poti.tok
Coloured dots scattered across a grid, each with a partner somewhere else on the board. Link every pair with a smooth path, fill every last cell, and let no two paths cross. Connecting the dots is easy; connecting them while covering the whole board is where the thinking lives.
Paths glow in their colour as you drag, snap to the grid, and trim themselves when you cross your own line, so experimenting never leaves a mess. A counter shows how much of the board is covered, and when the last empty cell fills the whole grid lights up. Sixty-six hand-built boards run from small and gentle to large and devious across easy, medium and hard, grouped into packs, with progress, best times and move counts kept. Drag to draw, tap to clear, undo whenever you want to rethink, and a limited hint lays down one correct connection when you are genuinely stuck. Slovenian and English, offline, no account, no advertising.
Tok on Google PlayHow to prove a board impossible without drawing a line
Colour the grid like a chessboard. A path steps between neighbouring cells, so it alternates dark and light all the way along: a path with both ends on dark squares covers exactly one more dark cell than light, a path between opposite colours covers equal numbers, and there is no third case. Now demand what this puzzle demands — that the paths together use every cell exactly once — and the arithmetic closes: (pairs with both dots dark) − (pairs with both dots light) must equal the board's own surplus of dark cells over light. On an even board that surplus is zero, so those two counts have to match exactly. A board that fails this cannot be solved by anyone, and you can see it at a glance, before a single path is drawn.
64cells, every one of which must be used
12dots placed on the board
6 + 6the dark/light split parity demands
25.0%of random scatters can even be legal
75.0%are impossible on sight
3.28 × 1012ways to scatter the dots at all
Not on this bench: no grid, no dots, no paths and nothing solved. The test it applies is necessary, never sufficient — a board can pass it and still be hopeless, and deciding the general case is genuinely hard: the full-coverage variant of this puzzle was shown NP-complete by Adcock, Demaine, Demaine, O'Brien, Reidl, Sánchez Villaamil and Sullivan in 2014. Parity is the cheap half of the problem, which is exactly why it is worth doing first.