The best alternatives to Gradients.app are Site Palette, Colorion, and Design Gradients. If these 3 options don't work for you, we've listed a few more alternatives below.
What do you think of Gradients.app?
Hurree— The smarter, simpler way to analyze your data
Site Palette is a browser extension to generate comprehensive palettes. A must-have tool for designers and frontend developers. Free colour scheme extraction
Gradienty is home to thousands of gradients created by you or a computer and posted every hour. Generate your own gradient or find the perfect gradient for your next project. Copy color hex codes or the CSS gradient code directly from the gradient.