Important
SymbiFlow is now F4PGA. See f4pga.org and f4pga.readthedocs.io.
FOSS Flows For FPGA¶
F4PGA is an Open Source solution for Hardware Description Language (HDL) to Bitstream FPGA synthesis, currently targeting Xilinx 7-Series, Lattice iCE40 and Lattice ECP5 FPGAs. Think of it as the GCC of FPGAs. The project aims to design tools that are highly extendable and multiplatform.
About F4PGA
Design Flows
Specifications
Appendix