Phosphor Icons
phosphoricons.com
Flexible open-source icon family with 1,200+ icons in six weights — thin, light, regular, bold, fill, and duotone — for React, Vue, and SVG.
Why it is useful
Icon sets often force a binary choice between line and fill variants. Phosphor's six weights give designers granular control over visual weight within a single cohesive system. The React package is particularly well-implemented.