Give SimpleD a Try.
No credit card needed. Just download and go crazy for 7 days.
Free 7-Day Trial
To start a 7-day free trial, just enter your email above and then click the download button to download the app. After downloading, double-click the installer file to install. No credit card or pre-payment required. You get seven days to make some awesome simple diagrams.
The trial is feature complete, and you'll be able to save your diagrams.
System Requirements
Behind the scenes, SimpleDiagrams uses Adobe AIR to make it easy for me to make a great cross-platform app. So if you want to know the base system requirements for SimpleDigrams, please review Adobe AIR's system requirements.