SYZYGY is a free to license interface specification for low cost, compact and high-performance connectors that economize the pin count available in FPGAs. See section Interface comparison in syzygyfpga.io for a reference of where does SYZYGY fit, between PMOD and FMC.
There are few development boards (carriers) and peripherals with SYZYGY connectors yet. An open source carrier design is ButterStick. However, there are PCB templates for KiCAD and Altium available for anyone to use (see SYZYGYfpga/pcb-templates).