nodo - Manage your daily tasks in the command line
Froala Design Blocks - 170+ free responsive design blocks based on Bootstrap 4
Simple Grid - Responsive & lightweight CSS grid for your website.
Webflow Flexbox UI Builder - Build flexible, responsive layouts — without writing code
Web Interface handbook - 200+ tips and tricks for creating a good web interface.
Antetype - Antetype - Layout aware User Interface Design - responsive and future proof.