We stopped selling Mockups for XWiki on November 1, 2013, and support and maintenance for the plugin ended November 1, 2014.
In accordance with our EULA, existing Mockups for XWiki customers will be able to continue using the plugin indefinitely, but they will no longer be eligible for support or updates.
If you would like to migrate to a different tool, we suggest using myBalsamiq. We are working on making myBalsamiq easy to integrate with, so that XWiki could build an integration between our two tools in the future.
We will be happy to give existing Mockups for XWiki customers significant discounts on myBalsamiq or Mockups 3 for Desktop if they wish to migrate their mockups there. Email email@example.com if you're interested.