Design for Humans - An email course about emotional design
TexturePacker - Texture Packer is hands down the best sprite sheet generation tool on the market.
Mobbin - Latest mobile design patterns & elements library
Free Texture Packer - Free Texture Packer is an open source tool that allows you to pack multiple images into one atlas for you games or sites.
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Sprite Monkey - Small and fast but still full-featured sprite sheet editor.