I am not a member of the FF or a Zeta, but I thought I would help you out
UT-Austin has
Kappa Delta and
Zeta Tau Alpha
KD does a Halloween Carnival with the Pi Phis (
see pics)
ZTA has a Backyard Bash with AChiO and a Fiesta with TriDelta.
I don't know of any events that they hold together, but some of the events above are a product of proximity of the houses to each other.
Kappa and Pi Phi hold Monmouth Duo events.
I would love to have Alpha Gamma Delta and Gamma Phi Beta back on campus so that Alpha Phi could have Syracuse Triad events.