GHDL is a complete VHDL simulator, using the GCC technology. GHDL implements the VHDL language according to the IEEE 1076-1987 or the IEEE 1076-1993 standard. GHDL compiles VHDL files and creates a binary which simulates (or executes) your design.
New GHDL development is at http://sourceforge.net/projects/ghdl-updates/ and includes significant VHDL-2008 support (in ghdl-0.33, released Oct 2015).
The original ghdl page was : http://ghdl.free.fr/
The original download page was : http://ghdl.free.fr/download.html