Both Xilinx and Altera^H^H^H^H^H^HIntel provides gratis tools for their lower end FPGAs, but those are plenty to implement an SoC, even one that can boot Linux.

Both Xilinx and Altera^H^H^H^H^H^HIntel provides gratis tools for their lower end FPGAs, but those are plenty to implement an SoC, even one that can boot Linux. In particular Cyclone V A9 is a pretty impressive FPGA. Sadly, Intel decided to _not_ provide gratis support for their Cyclone 10 GX :(