To create vector graphics for your app mock ups and icons, you might already be using Adobe’s Illustrator. If you think you’re spending too much monthly rentals to Adobe for the same, here is an alternative..switch to Inkscape!
Inkscape provides almost all the functions as in illustrator and it’s totally free!
Inkscape and illustrator has the same tools but with different names, here are a few of them to make you comfortable start using Inkscape!!