Proteus PCB design - Proteus PCB design combines the schematic capture and ARES PCB layout programs to provide a...
KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
Altium PCB Designer - Altium offers a top-notch, best-in-class PCB Designer to give engineers the tools they need to interlink with each side involved in the electronic design process.
PADS PCB Design - Best-in-class PCB design tools at unbeatable prices
upverter - Upverter makes it easy to design and share electronics on the web.
Proteus - Proteus - Proteus is a great electrical suite for circuit simulation purposes. You can simulate a single processor or multiple ones at the same time. The application is a great alternative for Virtual System Modelling.