ModelSim is a multi-language environment by Siemens[1] (previously developed by Mentor Graphics,[2]) for simulation of hardware description languages such as VHDL, Verilog and SystemC, and includes a built-in C debugger.
[6] Mentor HDL simulation products are offered in multiple editions, such as ModelSim PE and Questa Sim.
Questa Sim offers high-performance and advanced debugging capabilities, while ModelSim PE is the entry-level simulator for hobbyists and students.
[2] Questa Sim is used in large multi-million gate designs, and is supported on Microsoft Windows and Linux, in 32-bit and 64-bit architectures.
[8] ModelSim uses a unified kernel for simulation of all supported languages, and the method of debugging embedded C code is the same as VHDL or Verilog.