AaBbCc technically, yes, but why would you do that?
Flarum's backend represents at least 50% of the source code, you'll likely need a full team of developers to maintain an alternate code base. And none of the Flarum extensions would work with it unless you also rewrite the extension API and all of the extension's backends.
If you're trying to develop something else, you could re-use Flarum's Store and Mithril components for example, but there's also many other alternatives in the javascript ecosystem that are specifically developed to be re-used.
If you're trying to connect Flarum to some other code base, you could consider interacting with the Flarum REST API, and respectively use our PHP extension API to call webhooks on your other service.
