Ninja

Fruit Ninja, without much argument. It's the most recognisable, the controls take about three seconds to learn, and it sets up the timing that most of the others assume you already have.

Rarely. Most are precision games in ninja clothing - throwing, slicing or jumping accurately. Ninja: Bamboo Assassin is the closest here to genuine sneaking rather than aiming.

Moving targets and physics. In Ninja vs Ragdolls: Sharp Knife Throw! the target reacts to being hit, so a throw that would have connected a moment ago no longer will - you're leading a target, not aiming at a static one.

Very well. Slicing games in particular were built around swiping, so a phone or tablet is arguably the better way to play them compared with dragging a mouse across a screen.

Yes, every one of them runs free in your browser with no download and no account needed before your first throw, on desktop or on a phone.