What just happened? The American financial services company, best known for offering commission-free trades of stocks and exchange-traded funds, has filed the necessary paperwork with the US Securities and Exchange Commission to list Class A common shares on the Nasdaq under the ticker symbol "HOOD."

Robinhood hasn't yet said how many shares will be offered, nor has it confirmed the price range for the offering.

In the SEC filing, Robinhood said it plans to set aside between 20 percent and 35 percent of its shares for sale to Robinhood customers on its platform.

Robinhood in its SEC filing revealed that it had 18 million retail clients (or funded accounts) as of March 31, up from just 12.5 million at the end of last year. Collectively, it is holding nearly $81 billion in customer assets.

Robinhood has been in the news a lot this year, although not always in a positive light. Just yesterday, Robinhood was ordered by the Financial Industry Regulatory Authority (FINRA) to pay roughly $70 million in penalties for "systemic supervisory failures" and causing harm to millions of customers. It's the largest financial penalty ever ordered by FINRA.

The company came under fire over its role in the GameStop trading frenzy earlier this year and has been dealing with the fallout ever since. In the SEC filing, the company said its CEO's cell phone had even been seized by the US Attorney's Office as part of its investigation into the matter.

Image credit dennizn, zhu difeng