Microsoft has released daily test builds for Windows 7 and Windows 8.1 for its new Chromium-based edge browser. These can be found in the so-called Canary Channel. These browser builds are generated automatically almost daily, so they are similar to the Firefox Nightly builds. Accordingly, caution is advised when using.
The initial testing is done by the users and developers who download the builds. It is the first level of quality control and the opportunity for Microsoft developers to try new features. Non-use in productive use goes without saying.
Stable are only the builds of the dev channel. They are generated weekly but are not yet ready for Windows 7 and 8.1. That should not take much longer. The dev builds are more stable and have been tested by the Edge development team prior to release. For Windows 10 and MacOS, these builds have been around for some time. But these Dev versions are still early trials.
There will be a beta version in the beta channel, which is also called preview. This is generated every six weeks. However, the developers have not yet decided to issue beta versions. The Windows 10 builds have been around since the beginning of April 2019. The Mac versions are distributed since the beginning of May.
End of 2018, Microsoft had announced that it would replace its own HTML engine EdgeHTML by Chromium.