PwnageTool 5.0.1 is a Mac based iPhone firmware creation tool that will create custom ipsw files for various Apple devices that run the iOS operating system.
 
This version supports many devices in the Apple iOS family, as always this release may have specific instructions that need to be carefully followed to ensure that your device operates correctly. Information about this can be obtained at our blog. 

For more specific details please visit http://blog.iphone-dev.org and read the latest PwnageTool post that is linked from the sidebar. 
 
If you are new to this application please take the time to read the comments below the blog post as the answers to many common problems are discussed there.