Microsoft is making available promised test builds of its Chromium-based Edge browser for Windows 7, Windows 8 and Windows 8.1 today, June 19. These are Canary channel builds, meaning they will be updated daily.
Microsoft plans to add Dev channel builds for all these platforms "soon," according to today's blog post. Microsoft already offers Canary and Dev channel builds for Chromium-based Edge on Windows 10 and the Mac.
Microsoft has not committed definitively to bringing Chromium-based Edge to Linux, but has hinted that this will likely happen at some point.
As Microsoft notes in its blog post, the first Canary builds have some known issues, including lack of dark-mode support and no support for Azure Active Directory sign-in, which Microsoft is hoping to resolve "soon."
Chromium-based Edge for Windows 7 leaked a few months ago. I've been running it on my Windows 7 PC since then and it has worked well. (Calm down, people, I also have Windows 10 PCs and am running Chromium-based Edge, or Chredge, as I like to call it, there as well.)
In December 2018, Microsoft revealed plans to create a new version of Edge by using Chromium combined with some components currently in Edge, all in the name of providing greater browsing compatibility across the web. At that time, officials said Microsoft planned to make the new Edge browser available on Windows 7, 8.1, 10 and MacOS.. While Edge will continue to ship with Windows 10, Microsoft finally will be updating it independently of the operating systems on which it runs, meaning it will be updated and patched more frequently than the non-Chromium-based MSHTML version of Edge is currently.
Microsoft is bringing Edge to older versions of Windows and the Mac in the hopes of simplifying testing for developers who need to make sure their apps and sites work across all different operating systems and Windows variants.
If you're wondering how Chromium-based Edge will differ from Google's Chrome browser, here's a list of Google services that Microsoft has replaced or turned off in developing the product.