The "purpose"? To hurt people, relatively quickly.
It's not terribly close to anything you list in terms of stylistic similarities, but it depends a lot on which version of Silat you're discussing. E.g., Maphalindo silat (Guro Dan) is different from a "purer" strain.
My silat training has been mostly empty-hands, but as with kali, most techniques work equally well with weapons. Some moves assume you're wearing finger knives or holding a karambit.
As Sean says, footwork plays a large part in silat, although I'd argue that footwork plays a role in any art that does horrible things to opponents at close range. Unbalancing an opponent can only happen in so many ways--but IMO silat focuses on it in a different way than, say, Aikido.
Interestingly, for me, the closest thing to it that I have practiced was actually taiji, which surprised me quite a bit, but again, it depends on how one has studied taiji, which style, and with who.
Note also that the term "silat" may also encompass a bunch of non-martial arts cultural stuff, from dance to mysticism. The former is relevant to the martial art, the latter... is not.