Are there bindings for Unity, message menu and notification, couchdb and so on?
Depending on what you are trying to do, you could just build the app like any HTML + JS app and then throw it into a Webkit view. It's extremely simple to do in python:
The only python code you really need to pay attention to here is the code from
To run this make sure
As far as accessing the platform directly, you should check out Seed.
Well you could include a language that can run shell commands like php and this way take advantage of stuff like installing apps from a webpage and executing some commands (Like detecting which theme to use and what CSS to use depending on the system theme). For example you have this two questions which might help:
Can a server handle simultaneous shell commands? (Which talks about executing multiple commands)
Run a line command from a web (Clicking in a webpage link) (Which talks about clicking on a link and installing an app from the software center)
For a way to learn what theme is used you could parse the ubuntu file where it has the value for the default theme and depending on it modify the CSS of the site to reflect the new theme.
Questions about theme and where to find it can be found here:
All of this (and more if you use the search) help you know where to look when parsing and what files you can check to see what theme the system is using and what to use in the web page then.
Yes, you can write apps in pure html/css/js and yes binding are available for JS using GObject introspection. Take a look at GnomeSeed https://live.gnome.org/Seed