Google's Material Design System is one of the most well-known design systems alongside competitors like Fluent and HIGs (Human Interface Guidelines). Material Design, being a standard set of rules, guidelines, components, and rules for creating websites and apps, has set the standard for websites and web apps online. When I was a student, reading it for hours helped me understand user interface design deeply with clear guidelines. Review collected by and hosted on G2.com.
Arguably, Google's Material Library is more for Android, while HIGs is made for Apple. Personally, I'm a fan of Apple products, so HIG Design System is something I'm more used to visually. However, Google Material is sequenced, categorized, and paced well, so that makes learning and consuming it easy. Another point is that following the Material Library guidelines may result in your app looking "Google-y," which has its pros and cons. Cons being that it might look like Google's apps without the Google brand, which would seem odd. Review collected by and hosted on G2.com.