flask : how to architect the project with multiple apps?

Use blueprints. Each one of your sub-applications should be a blueprint, and you load every one of them inside your main init file.

Answering your second question

from flask import Flask
app = Flask(__name__)

You should put this into facebook/__init__.py

BTW, my runserver.py and settings.py always resides one level under facebook/.

Like this:

facebook/
         __init__.py
         feed/
             __init__.py
             models.py
             business.py
             views.py
         chat/
             __init__.py
             models.py
             business.py
             views.py
         games/
             __init__.py
             models.py
             business.py
             views.py
         common/
             common.py

runserver.py
settings.py

Content of runserver.py:

from facebook import app
app.run()

I suppose the content of settings.py should not be explained.

Content of facebook/__init__.py:

from flask import Flask
app = Flask(__name__)
app.config.from_object('settings')
from blog.views import blog #blog is blueprint, I prefer to init them inside views.py file
app.register_blueprint(blog,url_prefix="/blog")

I have tried blueprints and came up with a solution which works for me, let me know if you have other ideas.

Project Structure

facebook/
        runserver.py
        feed/
            __init__.py
            views.py
        chat/
            __init__.py
            views.py

Code

# create blueprint in feed/__init__.py
from flask import Blueprint

feed = Blueprint('feed', __name__)
import views

# create blueprint in chat/__init__.py
from flask import Blueprint

chat = Blueprint('chat', __name__)
import views

# add views (endpoints) in feed/views.py
from . import feed

@feed.route('/feed')
def feed():
    return 'feed'

# add views (endpoints) in chat/views.py
from . import chat

@chat.route('/chat')
def chat():
    return 'chat'

# register blueprint and start flask app
from flask import Flask
from feed import feed
from chat import chat

app = Flask(__name__)
app.register_blueprint(feed)
app.register_blueprint(chat)
app.run(debug=True)

In Action

 * Running on http://127.0.0.1:5000/
# Hit Urls
http://127.0.0.1:5000/feed # output feed
http://127.0.0.1:5000/chat # output chat