1. This is a cambrian explosion of open-source infrastructure tools
2. This is the dark ages of open-source UI
I think it's important to be aware that on this front the Open Source movement has completely stalled. When I was in College, I used Abiword, Evolution, and Rhythmbox. Now those things have been replaced for me with Google Docs, Gmail, and Amazon Music.
I love the web, it's incomparable for convenience, data protection, and access on multiple devices. But it is fundamentally at odds with Open Source software. Back in the day of desktop software, you could throw a tarball on the web and people could use your stuff without any real handholding. In order for people to use a web service you write, you have to maintain a server instance. It's just not worth it for me, random open source web service author, to maintain a server for millions of you, random open source software users. It's time and it's money for very little direct benefit to me.
And on app stores, it's pretty bad too. Maintaining a reviewed and updated app in an app store is a huge job, and not something a casual contributor to an open source GUI is going to want to do, just to have access to their branch of an app. And I'm not even sure Apple will let you submit an identical app with just one little feature changed.
This will change... the endgame is something like Ethereum, and the currentgame is maybe something like Heroku Button, but there is still a lot of infrastructure to build to make it as easy to maintain an open source web app as it is to maintain a desktop app.
And in the meantime, Open Source UI is just going to languish a bit. That's OK, it's just where we are in the history of the web. But it's going to get a lot better in the not too distant future.