Edit: i'm obviously talking about open source plateform.
PHP was popular for ages, and loads of great things were built on top of it. With modern development practices and improvements in the language, it's even possible to build better tools using it. But it's not like it's easier to build excellent tools than any of the other environments available – Rails, or Django, or Play, or whatever.
I don't think the development toolset would have any impact on the success or otherwise of the project, at the end of the day. Sure, maybe it would be a problem if it were some rarely-used, obscure system, but that hardly applies to Rails.
PHP is a better choice for web software that users are expected to host themselves.
Using PHP lets your users tap into the absolutely ginormous ecosystem of PHP hosting providers out there, and makes deployment dead simple ("FTP these files to that place, now you're done"). No other platform makes these steps as simple and inexpensive as PHP does.
If you're writing an app that you're going to host for the users, it doesn't matter much what you write it in. If you're writing an app that users are going to host for themselves, it matters a lot.
I think it does if you expect people to install that project.
(We'll have Diaspora on there soon...)
You need to significantly update your knowledge of the current state of web tools, then. All the world isn't Wordpress and Drupal.
The OP genuinely ha a good point.
Diaspora needs to be as easy to install as Wordpress and as ubiquitous, and then it would gain real adoption. Sad, but true.
Check out the Diaspora install instructions for Ubuntu: https://netenberg.com/fantastico.php#fantastico-scripts.html
It starts off with:
The install is a bit complex, but we're here to help.
It's extremely helpful to have some experience in Linux/Unix server
administration or Rails app deployment already. But don't worry, if you
run into problems and need help, just visit us in our IRC channels on
Freenode.
So is your point that velocity was held back due to lack of contribution? They have 300+ contributors; I'm uncertain that they'd get more if it was in PHP, and one could argue development would move slower.
By your logic, ColdFusion (or an open source variant like Railo) would have been a better choice, given the many CMSes and other open source project written in CFML (MangoBlog, blogCFC, ContentBox, Mura, etc). Heck, another vote for it would be the fact that MySpace was originally written in CF.
Personally, I find the whole language thing to be comparable to saying a restaurant failed because they offered Pepsi instead of Coke.
Rails, specifically has Github, Twitter, Basecamp, and Discourse, just off the top of my head.
https://www.reddit.com/r/IAmA/comments/1jg781/i_am_matt_mull...
It isn't hard to host a Rails app, but it's certainly harder than hosting one in PHP. Especially if you have little or no technical expertise or aren't willing to pay for anything more than shared hosting.
I think PHP in general is popular because it's made for web and very easy to get started. This has cause a disproportional market share where the bulk of the popular site, cms, project are PHP. But that doesn't necessarily means other languages can't compete, it just mean PHP have a good market share.
Another arguably popular website is OkCupid and that was coded in C++.
I also think PHP will stay popular because of Facebook. They have contributed to several important projects including a pretty good VM and there are a resurgent of momentum imo. Most of it are copying what RoR group have pioneer.
So to clarify, you're comparing Diaspora an open source p2p social media platform that is written in Ruby/Ember to what now?
I don't know any popular p2p social plateform written in PHP. All I know is the one written with Rails isn't as popular as it should have been.
pencilblue.org is a node CMS I just read about today, but... in general, for wide adoption, PHP is still king, and even 3 years ago, it was pretty easy to predict it would be king in 2015. I'll even predict its kingship for another 2-3 years. containerization and virtualization may play a part in its downfall over the next 2-5 years, but PHP will remain one of the major widely deployed systems for a long time (and PHP7 will likely strengthen that hold).