Free!
Excellent PC graphics program, basically the version of Sketch for Windows. It also opens Sketch files!
Free with limitations
Graphic design tool designed for web and apps, a bit too limited in the free version.
Free with limitations
Excellent program for graphic design and prototyping with a focus on team collaboration and web experience. A reference point.
Free!
Interface design and prototyping software by Adobe. Lately It has become totally free. It started a few years later than his competitors but it is growing steadily. Great.
Free!
Vector graphics tool, easy to use with good features. Great for newbies to begin draw with vectors.
Free with limitations
Great vector graphics editor, rich clip-art vector and template libraries. Not suitable for high definition printing.