As far as I can tell, Lattice products are the best if you're interested in using F/OSS tools. Yosys / Icestorm supports the Lattice ICE40 and ECP5 devices. QuickLogic also apparently do some officially supported F/OSS stuff for their devices, but I don't know much about them. Think I might have ordered one of their dev boards a while back, and then promptly put it on a shelf and still haven't gotten around to touching it. :-(

The problem is, none of these devices can match the raw performance of the devices from Xilinx / Altera / Microchip / etc. So you're kinda limited if you are trying to do something that needs serious horsepower.