The move comes weeks after several Indian firms decided to pull out of the project due to concerns that the app does not provide equal access to information, one of the principles of net neutrality.
Under Zuckerberg's plan, developers will be allowed to create new apps and experiences for Internet.org, which is filled with access to some news sites, health information, job postings and of course, Facebook.
Facebook partners with a mobile operator in each country to roll out the app.
Developers who want to be included in the Internet.org experience will have the chance to create experiences that adhered to the initiative's technical specifications -- which stress simple and data efficient websites.
Websites do not pay to be included in the Internet.org app and developers are not charged for the data people use to access their sites.
"Because these services have to be specially built to these specifications, we started by offering just a few," a Facebook blog post said. "But giving people more choice over the services they use is incredibly important and going forward, people using Internet.org will be able to search for and use services that meet these guidelines."
Zuckerberg last month addressed the uproar, writing that he fully supports the principles of net neutrality.
"But net neutrality is not in conflict with working to get more people connected. These two principles -- universal connectivity and net neutrality -- can and must coexist," he wrote. "To give more people access to the internet, it is useful to offer some service for free. If someone can’t afford to pay for connectivity, it is always better to have some access than none at all."
The Internet.org initiative was launched in 2013 with the goal of bringing mobile Internet access to people in the developing world -- pushing forward Zuckerberg's goal of connecting the world