gscc stands for GNU SystemC Compiler Collection, witch is a set of tools to manipulate systemc code ( systemc is a hardware description language www.systemc.org ). The most notable tool is called gsc, witch is a systemc to verilog translator.
Verilator converts synthesizable Verilog HDL modules into SystemC modules. This enables users with Verilog code to have a publicly available co-simulation environment. For all information, see http://www.veripool.com/verilator.html.