It's a traditional proprietary toolchain (about ~900MiB .tar.gz) that uses Synplify for synthesis and a custom fork of VPR for place and route, IIRC. It's reasonably easy to use and most of the UI flow can be scripted by Python, too, which is pretty nice. It's roughly comparable to something like Lattice Radiant or Lattice Diamond in terms of scope and features, IIRC, not Quartus/Vivado level.

I haven't updated my toolchain in a while so some of this may be out of date.

Small correction, the synthesis tool isn't Synplify.