If you want to use Yaffs on an Open Source project, then go ahead and download the GNU General Public Licence v.2 now. You can get it straight away from the link on the right of the page.
Yaffs is also available under a Commercial Licence for projects that don't want to disclose their source code. This Licence does not have the obligations of GPL, but is perpetual, world-wide, non-exclusive and carries no continuing royalty.
You can use the Open Source code to investigate and evaluate Yaffs, then before shipping your product to anyone outside of your organisation you buy a licence from Aleph One which does not have the GNU GPL obligation to release your Source Code. Contact sales@aleph1.co.uk for more information or have a look at our licensing information.