Best Free Open-source Sketch, Wireframe, Prototyping and Mockup Software

Hello, recently I found this amazing free desktop application for prototyping named Evolus Pencil.

Here is some features of the software:

1. Free and opensource, you don’t have to spend money to get it.
2. Cross-platform, it’s available for Linux, Windows and Mac OSX, and even as Firefox Extension
3. Create wireframe for your design easily with pre-built shapes, including common desktop and mobile UI.
4. You can also use it to draw diagram and flowcart.
5. Well-crafted application, I have used it many times and no problem so far.
6. Export drawing to various format, including PDF, SVG, HTML, PNG and OpenOffice document (ODT)
7. Easy, you do not need to read documentation to use it.
8. Light and fast, it runs smoothly on my 4GB systems.
9. Built-in clipart browser, you can insert free clipart from Openclipart.org directly to your canvas.
10. And manymore.

Some screenshots:

Evolus Pencil Interface

Insert clipart

	<div id="gallery-1" class="gallery galleryid-1313 gallery-columns-2 gallery-size-thumbnail"><dl class="gallery-item">
		<dt class="gallery-icon landscape">
			<img src="/images/2013/09/evolus-desktop-xp-and-ext-js-widget-150x150.jpg" alt="Evolus pencil desktop XP and EXT widget" title="" class="rounded-lg my-6 max-w-full h-auto shadow-md" loading="lazy" />
		</dt>
			<dd class="wp-caption-text gallery-caption" id="gallery-1-1322">
			Evolus pencil desktop XP and EXT widget
			</dd></dl><dl class="gallery-item">
		<dt class="gallery-icon landscape">
			<img src="/images/2013/09/evolus-android-and-ios-ui-kit-150x150.jpg" alt="Evolus Pencil Android and IOS UI kit" title="" class="rounded-lg my-6 max-w-full h-auto shadow-md" loading="lazy" />
		</dt>
			<dd class="wp-caption-text gallery-caption" id="gallery-1-1321">
			Evolus Pencil Android and IOS UI kit
			</dd></dl><br style="clear: both"/><dl class="gallery-item">
		<dt class="gallery-icon landscape">
			<img src="/images/2013/09/evolus-flowcart-and-fontawesome-150x150.jpg" alt="Evolus Pencil flowcart and Fontawesome icons" title="" class="rounded-lg my-6 max-w-full h-auto shadow-md" loading="lazy" />
		</dt>
			<dd class="wp-caption-text gallery-caption" id="gallery-1-1323">
			Evolus Pencil flowcart and Fontawesome icons
			</dd></dl><dl class="gallery-item">
		<dt class="gallery-icon landscape">
			<img src="/images/2013/09/evolus-pencil-shapes-150x150.jpg" alt="Evolus Pencil common shapes" title="" class="rounded-lg my-6 max-w-full h-auto shadow-md" loading="lazy" />
		</dt>
			<dd class="wp-caption-text gallery-caption" id="gallery-1-1324">
			Evolus Pencil common shapes
			</dd></dl><br style="clear: both"/>
	</div>

My comment of this software: It does what it should, no bullshit.