Line and filled pairs for the same metaphor. The current terms are the Remix Icon Licence, not Apache 2.0: free to use in products, but not to resell as a standalone icon pack.
Open SVG scenes you can recolour in the browser. Free for personal and commercial work, with no attribution, under the project's own licence. Redistributing the set or using it to train models is not allowed.
Free photographs for personal and commercial projects under the Barnimages Licence. You may not sell the photo itself as a print or merch; credit is not required.
A mixer for illustration libraries by independent artists. The Blush licence allows commercial use in an end product, but not resale of the illustrations themselves or merchandising them as-is.
Illustration and icon packs. The DrawKit licence grants royalty-free use in your own commercial and non-commercial work, subject to the full terms on the site.
Free PSD mockups, textures and UI kits. The site licence allows personal and commercial use, and does not require attribution, but you may not redistribute the files on their own.
The free section of Pixeden's mockup and template library. Free items are royalty-free for personal and commercial work; redistribution of the source files is not allowed.