Flowee

Flowee began as a mini-game designed by Rob Clewley for OPERANDi, a science fiction hacking game he is working on; the standalone version was built in Unreal Engine by Pumashock, who also wrote its music. It is free to play in the browser on itch.io, with a name-your-own-price download for Windows and macOS that works offline and includes the soundtrack.

Each puzzle gives you a set of sources, each labelled with a power value, and a row of target values. You place sources, sum nodes and sinks on a small 3x4 grid, then click the pipes between neighbouring nodes to turn them on. A source can feed several outputs, and each one receives its full value. A sum node merges whatever flows into it and points its output at a sink. A sink shows the total of everything that reaches it, and the puzzle is solved when the sinks match all the targets.

The challenge is partly arithmetic and partly layout: there are only twelve cells, so finding a combination that adds up is not enough if the pieces cannot be placed next to each other. Some puzzles have more than one solution. Illegal set-ups, such as a sum node pointing at something other than a sink, are marked in red until you fix them.

Three puzzles arrive each day, easy, medium and hard, so it suits both a quick warm-up and a longer think.