NI Multisim

From National Instruments:

Multisim is an industry-standard, best-in-class SPICE simulation environment. It is the cornerstone of the NI circuits teaching solution to build expertise through practical application in designing, prototyping, and testing electrical circuits. The Multisim design approach helps you save prototype iterations and optimize printed circuit board (PCB) designs earlier in the process.With Multisim, you can optimize your circuit design performance with powerful SPICE simulation and intuitive analyses. You can reduce design errors, prototype faster, and improve productivity. Save prototype iterations and optimize printed circuit board (PCB) designs earlier in the design process by using the Multisim design approach.

View larger image