Arcticons (Arctic icons) is a line-based icon pack forked from Frost but rebuild with consistent sizing and adjustments specifically for lines in mind. Arcticons is FOSS and provides mostly icons for open-source apps on F-Droid (but there are many other apps in this pack too). The design is simple and clean with minimal lines that give you a nice see-through effect.
Download
Two versions for the dark- and lightmode user, available to download from F-Droid, Google Play & Github!
Arcticons Dark
Arcticons Light