Electron – Build cross-platform desktop apps with JavaScript, HTML, and CSS
electronjs.org
electronjs.org
On the subject of bloat and package size, neither of these matters to the user. Electron apps run fast enough for users on the hardware they have. Users care much more about ease of installation and ease of use -- which are the key deliverables when you use web technologies wrapped in Electron.
Sometimes taking shortcuts is fine, your users might prefer additional features over performance and polish. But if you are a company the size of Slack, maybe you can afford not to take shortcuts or do those sacrifices while claiming it's "good enough".
"Good enough" is different from "good".