As some of you may have noticed, I've been obsessed for many decades with having open FPGA bitstream documentation so that people can write their own FPGA designs tools, especially FLOSS (Free-as-in-Liberty Open Source Software).
I recently found out about IceStorm, a project that has somehow reverse-engineered and documented the Lattice iCE40 FPGA. They've actually put together a fully-open-source tool chain with Yosys for Verilog synthesis and Arachne_pnr for placement and routing. I don't know how usable or robust the tools are. I'm planning on taking a close look starting next month.
If you're interested, here's the IceStorm link, which has links to the other tools: Project IceStorm
Discussion of Yosys and the tools is at reddit: Yosys Open SYnthesis Suite
Update: Here are a couple of nice Hackaday items about IceStorm:
From 29 March 2015: Reverse Engineering Lattice’s iCE40 FPGA Bitstream | Hackaday
From 29 May 2015: An Open Source Toolchain For iCE40 FPGAs | Hackaday
Update 2: Here are some good IceStorm installation instructions: Projet IceStorm : le FPGA libéré ! | Front de Libération des FPGA. They're in a combination of French and GNU/Linux.
Here's the Lattice IceStick directly supported by IceStorm: Lattice Semiconductor: ICE40HX1K-STICK-EVN iCEstick Evaluation Kit. It's US$20.89 in the USA.