[snvzz]

Open synth/route stack supports Lattice iCE40 and ECP5 the best.

iCE40 are a relatively simple, cheap and easy to work with architecture with a focus on low power usage. iCESugar + nanoDLA (cheap sigrok-friendly logic analyzer) is a good cheap set to get started on FPGAs with. These are cheap on aliexpress.

ECP5 are much larger, much more complex and powerful enough to fit a whole computer (e.g. the minimig open Amiga implementation) in. I don't recommend going anywhere near this until you've already got started with iCE40, but a high-density and price-effective development board is the ULX3S.