Here's how it goes:
To start off with, we choose a set of keys (i'm thinking on the piano, but i don't know, it might work on other instruments too), and we only work within that set. For example: one set would be all the notes in C major (i.e. all the white keys). Anyway, the first poster would choose a chord (a three-note chord) that is possible to make in that key, and they would also tell whether it was in the root position, the 1st inversion, or the 2nd inversion. Then the next poster would make it into a different chord by moving one note one space over.
Example: (For this example we're working in C major)
First poster: C major, root position
Second poster: A minor, 1st inversion (by moving the G in the first poster's chord up to A).
And so on.
Okay, i'll start. Let's work in F major (i.e. all white keys except for B, which is a flat in this key).
D minor, root position (i love D minor!
)