Simple canvas demo application
This app creates a database to locally store account details which can be used to display on a Salesforce account page. (/app/home.action)
There is also a component that is for display in a visualforce tab that simply decodes and displays information from the Signed Post (/app/display.action)
Read the Salesforce Canvas Developers guide to find out how to get canvas running first locally, then on Heroku. http://www.salesforce.com/us/developer/docs/platform_connect/index_Left.htm