A prototype design software mockups for desktop is recommended.

Similar to graffiti, it's easy to get started. You can check it out.

Storage:Say goodbye to the pile of paper wireframes...
Ease of use:The UI control supports automatic drag and drop and automatic alignment;
Appearance:Hand-painted style, simple and refreshing;
Diversified:From buttons to input boxes, from navigation bars to pages, tables, and even the most popular iPhone elements;
Convenience:In addition to the toolbar, you can also use the hidden edit box to modify elements. Shortcut Keys are supported;
Compatibility:You can save elements in XML or export PNG images to any project;
Cross-platform:Windows, Mac OS, and Linux can be used, and versions that can be integrated into confluence, Jira, and xwiki can be used. By the way, if you do not have time to download the desktop version, you can also directly use the web version of balsamiq mockups...

The trial version is 7 days, but the author provides multiple channels to obtain the key

Http://www.balsamiq.com/