Someone mentioned on the forums that searching for Edge Code extensions doesn’t bring up much of a list. Luckily because Edge Code is a distribution of Brackets, you can use nearly all of the Brackets extensions just fine with Edge Code.
So if you’re looking to extend Edge Code beyond it’s built-in functionality you can check out the list of Brackets extensions on the Brackets Github Wiki.
To install one of those extensions into Edge Code, simply download the extension (usually downloading a zip file of the project source is good enough). Then in Edge Code go to Help->Show Extensions Folder, copy the unzipped folder into that directory and reload Edge Code.
Right now not all Brackets extensions will work with Edge Code. Specifically there were some big changes between Sprint 19 and Sprint 20 in Brackets that changed some of the APIs. The next release of Edge Code will include those changes so you’ll be able to grab all of the extensions that only work with Sprint 20.