Logo by ShapeFactory is a free and easy-to-use logo generator, that helps you create clean, simple, hassle-free logo designs.
Trianglify.io is a tool to generate low-poly, geometric (triangle) backgrounds, patterns, textures, and vectors, created by Quinn Rohlf.
CSS Gradient is a happy little website and free tool that lets you create a gradient background for websites.
CSS Matic offers great CSS tools and generators for web designers and developers. CSS Box-Shadow, Border-Radius, Gradients and more.