GHDL is an open-source simulator for the VHDL language. GHDL allows you to compile and execute your VHDL code directly in your PC.
GHDL fully supports the 1987, 1993, 2002 versions of the IEEE 1076 VHDL standard, and partially the latest 2008 revision (well enough to support fixed_generic_pkg or float_generic_pkg).
By using a code generator (llvm, GCC or a builtin one), GHDL is much faster than any interpreted simulator. GHDL runs on Linux, Windows and Apple OS X. You can freely download a binary distribution for your OS or try to compile GHDL on your own machine.