Re: ESL
ESL is a Mentor Graphics flow of designing digital circuits in a level higher than RTL. because it is more easy to set your design in C/C++ or systemC when your design is more complex and large. so in ESL you can build your design using C/C++ or systemC or even M-files of Matlab. you can verify and simulate your design then using questa. also you can use mixed designs of RTL or systemC.
ESL flow contains the following tools:
Visual Elite: the environment in which you create or put your design.
Vista:the tool that makes analysis of your design.
Catapult: the tool that synthesizes designs of C/C++ to systemC or VHDL/Verilog so that you can add it further into your design.
System Architect: that tools that converts your RTL code to SystemC.
Questa: for verification and simulation.