The ASRock Z97 Extreme4 comes with three PCI Express 3.0 x16 slots and three PCI Express 2.0 x1 slots.
The second and the third PCI Express x16 slots (PCIE5 and PCIE6) share bandwidth with the first one (PCIE2), which means that the first slot works at x16 speed if the other two are not used, but at x8 if either one of them is populated. They also share bandwidth among themselves, so if you install three video cards, the first one will work at x8 and the other two will work at x4. So, the possible slot configurations are x16/x0/x0, x8/x8/x0, and x8/x4/x4.
All the PCI Express 3.0 x16 slots support both SLI and CrossFireX technologies.
There is also a M.2 slot, supporting one SATA-600 or PCI Express x2 SSD module.