You mean you don't want to use the command line / composer client ? Have a look at the Pockethold installer and Bazaar, these are third-party tools you can use right now.
Saying you don't want to use Composer (the technology) would be pretty much the same as saying you don't want to use PHP, as it's one of the core technologies used by Flarum ?
There might come a time when the local composer client isn't required anymore and is replaced by a pre-packaged solution or a cloud composer client but that's likely not before stable ?
