Design is not just what it looks like and feels like. Design is how it works.
I can't call myself a designer yet but I am learning.
I do think design applies to everything I am doing. Even this wiki has some design choices of how it can be structured. As the quote above says, it's not how it looks like, it's how it works.
Findguidelin - The fastest way to brand assets.
Lona - Tool for defining design systems and using them to generate cross-platform UI code, Sketch files, and other artifacts.
Free Logos - Has some nice logos.
Design Languages - Curated library for design languages, design systems and front-end frameworks.