[duskwuff]

The toy you're referring to is a model of the wahrk gallows you encounter in the Jungle Island lake. It's implied that it's used to execute/sacrifice prisoners by feeding them to the carnivorous Wahrk that live in the lake -- the "actions" you're referring to are discrete steps of lowering the prisoner to be eaten!

The numeral system is really interesting in its own regard, too. It's written as base-25, but each digit is composed of two base-5 subdigits superimposed on each other at right angles in a square frame. (The subdigits are all designed in a way that makes this unambiguous.) For example, 0 is an empty square and 1 is a vertical line, so 5 is written as a horizontal line, and 6 is a cross.

The game uses 5 as an "arc number" -- Riven is the "fifth age", the main game area consists of five islands, many objects and locations in the game are five-sided, and the game was originally distributed on five CDs -- so it's only natural for the number system to operate on base-5 as well. :)

There's also an alphabetical writing system present in game, but it's used with a constructed in-game language (not just a cipher for English text), so players aren't expected to understand it.