Invision - Prototyping and collaboration for design teams
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Zeplin - Collaboration app for UI designers & frontend developers
Sketch - Professional digital design for Mac.
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.
Adobe Illustrator - Adobe Illustrator is a vector graphics editor.