I've just installed Flarum locally (OS X). Some quick notes on that...
1) I installed Composer in /usr/local/bin, so to use it globally.
2) I setup a virtual directory to run the site at /Site/discussion
3) When installing Flarum, the process interrupted at "Installing guzzlehttp/guzzle (6.1.1)". I had to get a GitHub token, which worked, and the process continued again to completion.
4) Your installation documentation (http://flarum.org/docs/installation/) doesn't make it clear that you need to create the database first. You should make that more clear so it's not a guessing game.
5) Your installation docs also don't make it clear what you mean by "server configuration block" when talking about "Nginx" and "Lighttpd", so I just ignored that part for now. Devs probably know what you mean, but none devs like me do not know, so you should make it more clear what file, specifically, needs edited in those cases. I can do these things If I actually know what to open and where to find it.
6) When first opening the Flarum install in a browser, I had to chmod permissions one a few locations. The instructions said use "0755", but I could not get this to take. I had to use "777".
After that I refresh the browser. I expect to see a default view of the Flarum front-end, but instead I see a UI full of errors. In the left column there are 26 errors (number 0–26). Most of them seem to have these in their paths: ".../vendor/oyejorge/...", ".../vendor/flarum/...", ".../vendor/zendframework/...".
A lot of the problems mention "LESS", but not only. If I click any of these items in the left column, they show a related snippet code in the body of the main screen. Means nothing to me. Might as well be Arabic.
In the top of the screen is another error, this:
Less_Exception_Parser
Less.php cache directory isn't writable: /Users/me/Sites/discussion/storage/less/
So what's going on? I'm guessing part of the problem might be #5 above, concerning the "server configuration block", so if you can clarify what that means, I can start there. Anything else?