[Django]-How can I use one django app ( with one db ) in two projects ? ( Using my app as a service )

I think simplest solution will be:
django muliple databases + lets say, PostgreSQL DB allowing crossdomain access.
Create router for your blog app and use any db you want.

UPD:

Somewhere

# class for routing db operations for  some blog myapp
class MyAppRouter(object):
    """A router to control all database operations on models in
    the myapp application"""

    def db_for_read(self, model, **hints):
        "Point all operations on myapp models to 'other'"
        if model._meta.app_label == 'myapp':
            return 'other'
        return None

    def db_for_write(self, model, **hints):
        "Point all operations on myapp models to 'other'"
        if model._meta.app_label == 'myapp':
            return 'other'
        return None

    def allow_relation(self, obj1, obj2, **hints):
        "Allow any relation if a model in myapp is involved"
        if obj1._meta.app_label == 'myapp' or obj2._meta.app_label == 'myapp':
            return True
        return None

    def allow_syncdb(self, db, model):
        "Make sure the myapp app only appears on the 'other' db"
        if db == 'other':
            return model._meta.app_label == 'myapp'
        elif model._meta.app_label == 'myapp':
            return False
        return None

in settings.py

DATABASES = {
'default': {
     ...
     # Project DB
           }
# Blog DB
'blog': { 
    'ENGINE': 'django.contrib.gis.db.backends.postgis',
    'NAME': 'test',
    'USER': 'postgres',
    'PASSWORD': 'admin',
    'HOST': '111.111.111.111',
    'PORT': '5432',
    }
}

...
DATABASE_ROUTERS = ['path.to.MyAppRouter', 'path.to.MasterSlaveRouter']