Earlier quoted context omitted.
Steam always used a HTML renderer, even in its 2006 first incarnation. Nowadays it uses the same CEF (chrome library) as electron uses. So Steam was one of the first "Electron" apps. A very first one was Windows Explorer as of Shell update that came with Internet Explorer for Windows 95 (included by default in Win98). All the sidebars of Explorer were HTML based.
>A very first one was Windows Explorer as of Shell update that came with Internet Explorer for Windows 95 (included by default in Win98). All the sidebars of Explorer were HTML based. That's a stretch; X/SG/HTML user interface APIs are not the same as a whole browser with Javascript VM, full networking and security stack, full-featured/standards-compliant (X)HTML/CSS rendering engine plus support for legacy features,…
Also WinXP used a forked Trident engine with some removed features for "Software" dialog and various other features (Windows Help, etc).