A Verilog/VHDL killer.
1. http://raintown.org/lava/ 2. http://www.cs.bham.ac.uk/~singhsu/
There's also PSHDL from Karsten Becker[2] at TUHH. It's immature and seems to be focused on teaching at the moment.
[1] https://chisel.eecs.berkeley.edu/ [2] http://blog.pshdl.org/