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.
Haven't gotten very far yet but TinyFpga BX was easy to get set up and running "LED blink" which is the hardware version of hello world. I've used microcontrollers since forever and want to expand my options.
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.