A couple of friends said to me, "Look - that's not metaphysics! It's mathematics!". Ok. Fair enough - but then you can't have it both ways. Here we go with a list of the parts of modern mathematics invented by philosophers, in the period roughly 1879-1922:
1. The theory of relations.(Admittedly, mostly logic and foundations, and mainly Frege and Russell. There's overlap, of course, with Dedekind, Cantor, Peano, Zermelo; and somewhat later, Hilbert, von Neumann and so on. I have also ignored the Poles. Not on purpose. Mainly because I know much less about Lesniewski's work.)
2. The theory of quantification.
3. The analysis of what a variable is.
4. Truth tables/compositionality.
5. The formulation of formation and inference rules.
6. The recognition of the intimate relation of $A$ and "$A$ is true".
7. Higher-order logic.
8. The theory of types.
9. The theory of identity.
10. The concept of an abstraction principle.
11. The definition of cardinality.
12. The definition of ancestral (transitive closure).
13. The derivation of Peano's axioms from an abstraction principle (Frege's Theorem)
14. The recognition of some need for levels/types/orders.
15. Russell's paradox.
To be a bit more serious, maybe we should think of these as all simultaneously parts of mathematics, philosophy and logic.
I neglected to mention The Romans.