Fritzing is an open-source hardware initiative that makes electronics accessible as a creative material for anyone. We offer a software tool, a community website and services in the spirit ofProcessing and Arduino, fostering a creative ecosystem that allows users to document their prototypes, share them with others, teachelectronics in a classroom, and layout andmanufacture professional pcbs.

http://fritzing.org/home/

Another good alternative:

1. Eagle PCB – a PCB designer – http://www.cadsoftusa.com/download-eagle

2. Filter Lab – Filter designer – http://www.microchip.com/pagehandler/en_us/devtools/filterlab-filter-design-software.html

3. Filter Pro – Filter designer – http://www.ti.com/lsds/ti/analog/webench/webench-filters.page?DCMP=sva-web-filter-en&HQS=sva-web-filter-powerhouse-20140204-lp-en

4. LtSpice – Design Simulation – http://www.linear.com/designtools/software/