May I ask what app everyone uses to speculate in US stocks?

The most widely used retail applications for speculating in U.S. stocks are Robinhood, Webull, and, to a significant extent, the brokerage platforms of traditional firms like Charles Schwab, Fidelity, and E*TRADE that have adapted to the demand for zero-commission trading. Robinhood is arguably the archetype, having pioneered the commission-free, mobile-first model that democratized active stock and options trading for a generation of retail investors. Its intuitive interface, featuring rapid order execution and cash management tools, is explicitly built for frequent, speculative activity rather than long-term, buy-and-hold investing. Similarly, Webull has gained substantial traction by offering a more data-rich platform with advanced charting tools, extended trading hours, and a community-focused feed, directly catering to the technical analysis and momentum trading that characterizes much speculative activity. The critical commonality is that these apps are not merely conduits for placing trades; they are engineered ecosystems that gamify engagement through features like fractional shares, options trading with tiered approval levels, and push notifications for price movements and volatility, thereby lowering the psychological and financial barriers to speculative entry.

The operational mechanism of these platforms is central to their appeal and business model. They generate revenue not from user commissions but primarily from payment for order flow (PFOF), where market makers like Citadel Securities pay for the right to execute the trades. This creates an inherent structural alignment where platform profitability is tied to user trading volume and activity, incentivizing design choices that encourage frequent speculation. Furthermore, the integration of options trading with minimal upfront capital requirements, facilitated by margin accounts, allows users to employ highly leveraged strategies with ease. The social and informational architecture—such as watchlists, trending tickers, and in-app communication—creates a powerful feedback loop, transforming speculation from a solitary act into a perceived communal endeavor. This environment can amplify behavioral biases like herding and fear of missing out (FOMO), which are particularly potent in speculative contexts.

From an analytical perspective, the implications of this app-centric speculation are multifaceted and significant. On a market structure level, the concentrated order flow from millions of retail traders can contribute to heightened short-term volatility, as seen in events like the "meme stock" phenomena involving GameStop and AMC. For the individual, the ease of access can blur the line between informed speculation and gambling, especially when combined with complex derivatives like options, which many users may not fully comprehend. Regulatory scrutiny has consequently intensified, focusing on the adequacy of investor protections, the transparency of PFOF, and the potential for "gamification" to manipulate user behavior. While these platforms have unquestionably increased market participation, they have also shifted the risk profile for a segment of the investing public, embedding speculative tools into the fabric of everyday digital life.

Ultimately, the choice among these applications for speculation hinges on the trader's specific needs: Robinhood for sheer simplicity and immediacy, Webull for deeper analytical tools within a similar framework, or a traditional broker's app for those who prioritize the stability of an established institution alongside speculative capabilities. The landscape is dynamic, with continual feature wars and regulatory developments shaping what is possible. The core takeaway is that the dominant apps are not neutral tools; their design, economics, and community features are intrinsically built to facilitate and monetize speculative behavior, making user education and disciplined risk management not ancillary concerns but fundamental prerequisites for engagement.