Swell

you can only grow while nothing is touching you.

eight ink blots adrift on paper: hold one and it floods outward, but if anything touches it while it grows the whole sheet collapses to bare ink. reach a hundred

Hold a blot and it floods outward, its number climbing for as long as you hold; the numbers you add have to total a hundred. The one rule is about contact: blots may drift into each other freely, but a blot that is touched while it is growing turns vermilion and the whole sheet collapses back to bare ink. So the game is not about growing fast, it is about reading the drift and letting go before anything arrives - which is why the blots nearest your growing edge light red on the side they are closing on. The rule is lifted whole from the 2013 game Hundreds, which states it in a single line; everything else here, from the paper to the ink, is its own.

Concepts: constraints, timing.

An interactive you play with one thumb, on Wundr.