Online tool to draw saw lines for plywood?
Search term: Panel Cut Calcuator

A few results - most seem to be software to download and run, rather than a website. The first one does claim to work on the website, but I have not tested any of them personally. I think all the ones I'm linking claim to have a free, community, or functional demo version:

http://www.optimalon.com/online_cut_optimizer.htm

http://www.optimizecutter.com

http://www.maxcutsoftware.com

http://www.applicationprogram.net

http://cutlistplus.com

Enjoy.