SpaceChem-like [the Sequence] is free for the first time but you have to be quick
Only free today
Released in September of last year, [the Sequence] is best defined as a game that falls in the same category as Gold Award-winning SpaceChem.
Just as our own Christian Valentin puts it, "you need to transport a node from an input area to an output, in such a way that the process repeats without any collisions".
It gets increasingly complex from here but should be a little easier than SpaceChem.
In any case, there's really no reason not to check it out now that it's free for the day. It's also one of your only options as SpaceChem has vanished from the App Store due to compatibility issues.
And in case you're wondering, here's what the gameplay looks like: