Website that delivers content to social media websites

I'd like a website that has the following high level features:
- User registration capability
- Home page page for unlogged users
- Home page for logged users
- Another page that would serve as a dashboard to post things in different social media
- Dashboard should show all possible social media websites you can post to, implementation not necessary for all of them
- Implementation for posting content to twitter
- Capability of adding more social media websites
- Using open source tools, hosting in AWS S3 preferably
- Preferably with a Python framework