Zed currently uses IBM Plex Sans and Lilex as its default fonts, and the aliases .ZedSans and .ZedMono also resolve to these.
Zed Plex Mono was a fork of IBM Flex with ligatures manually added. It is no longer available as it conflicts with the open font license due to the use of "Plex" in the name. Zed Plex Sans was a re-packaging of IBM Plex Sans; and Zed Plex Mono was just like Lilex, but less good.
Before that, we used to use Zed Mono and Zed Sans, custom builds of Iosevka liscensed under the SIL Open Font License, Version 1.1.
They were built for use in Zed. Zed Sans uses a quasi-proportional spacing to allow the font to still feel monospace while not having such wide gaps in a UI setting.
See: ./zed-iosevka
