ExtraETF is a mobile platform for ETF and stock market analysis that gives investors tools for portfolio tracking and market research. The project centered on real-time updates, easy authentication, and premium subscription features.

Onboarding

Onboarding

News Page

News Page

Theme Page

Theme Page

Article

Article

Equity Page

Equity Page

Equity Details

Equity Details

The Challenge

When Isarvest GmbH approached us to build ExtraETF, they wanted a mobile application that would open up ETF investing through analytics and real-time market data. The app had to handle complex data visualization, live price updates, and premium features, and stay fast and pleasant to use on both iOS and Android.

Our Approach

We chose Flutter as the foundation for mobile development, so we could build once and ship to both platforms at the same time. That helped us meet a tight launch timeline without giving up code quality or feature parity. Flutter's widget system and rendering performance suited the financial charts and real-time data streams the app is built around.

For real-time price updates, we implemented a Go-based service that efficiently broadcasts live market data to both web and mobile clients. Go's concurrency model and lightweight goroutines manage thousands of simultaneous WebSocket connections with little resource overhead.

Technical Wins

Building features once and shipping them everywhere sped development up considerably. Hot reload shortened iteration cycles, and the single codebase removed a whole class of platform-specific inconsistencies.

The Go WebSocket service held up well in production: real-time price updates reached clients with low latency even as the user base grew, and the service stayed cheap to run.

Integration of native platform features—Apple and Google , push notifications, —went smoothly through Flutter's plugin ecosystem, so the app feels native on each platform without giving up the shared codebase.

Business Impact

The technology choices translated directly to business outcomes:

  • Six months from kickoff to both stores, with feature parity on day one — no staggered iOS-first launch and no platform waiting for the other to catch up.
  • reduced by an estimated 40% compared to running two parallel native builds — the number that falls out when the same work stops being paid for twice.
  • Around 99% of the mobile code is shared between iOS and Android; the platform-specific part is a few hundred lines of native glue for billing, OAuth, and push.
  • One engineering team owns the entire mobile stack, so maintenance overhead stayed flat where two native teams would each carry their own upgrade cycle.

The app launched on both the App Store and Google Play and has kept strong user retention, helped by its smooth performance and real-time data. The subscription model runs on the in-app purchase integration and brings in steady revenue, and the architecture has scaled with the user base.

Key Features

Push Notifications

Real-time market alerts and portfolio updates keep users informed about significant price movements, market news, and personalized investment insights. The notification system is built to handle high-frequency updates while maintaining battery efficiency and user preference controls.

Authentication & Social Login

Streamlined onboarding through Apple and Google OAuth integration provides users with secure, one-tap authentication. This reduces friction in the signup process and ensures account security through trusted identity providers.

Deep Linking

Universal links and app links take users from web content, email campaigns, and social media straight to specific screens in the app. Users can share ETFs, portfolios, or market analyses with each other.

Interactive Charts

Advanced charting capabilities display market data with multiple timeframes, technical indicators, and comparison tools. The charts are optimized for mobile interaction with pinch-to-zoom, gesture controls, and responsive performance even with large datasets.

Theme Support

Full dark and light themes follow user preferences and system settings, so the app stays comfortable to read in any lighting. The design system keeps both themes visually consistent and readable.

Subscription Management

In-app purchase integration for premium features with seamless subscription management through Apple App Store and Google Play Store. The system handles trial periods, subscription tiers, and restoration across devices.

FAQ

ExtraETF is a mobile app for ETF and stock market analysis built for Isarvest GmbH — real-time market data, interactive charts, portfolio tracking, and premium subscription features on iOS and Android. We built the mobile side with Flutter and the real-time data layer with a Go WebSocket service.
One team had to ship the same features to iOS and Android on a tight timeline, and a financial charting app needs to own its pixels — a real chart is custom rendering, not a stock UI widget. Flutter provides both: a single Dart codebase and a canvas to draw on directly. In the finished app around 99% of the mobile code is shared between the platforms, with only a few hundred lines of native glue for billing, OAuth, and push.
A Go-based WebSocket service broadcasts live prices to web and mobile clients, using goroutines to hold thousands of simultaneous connections with little resource overhead. Updates are conflated upstream to a steady cadence of roughly one update per instrument per second — the rate a human watching a price actually needs — which keeps latency low and client CPU and bandwidth sane as the user base grows.
Six months from kickoff to launch on both the App Store and Google Play, with feature parity between the platforms from day one. Compared to running two parallel native builds, the estimated time-to-market reduction was about 40%, because business logic, charts, and screens were written once instead of twice.
Yes — ExtraETF is chart-heavy by design, with multiple timeframes, technical indicators, and comparison tools. Because Flutter draws every pixel itself, the chart code runs identically on both platforms, and keeping the expensive geometry work out of the paint phase keeps interaction smooth within the 16.6ms frame budget even with large datasets.

ExtraETF was built with Flutter and Go as part of our Flutter app development service, and it is the reference build behind our fintech app development practice.

For the engineering deep-dive — how the Go WebSocket service fans real-time market data out to thousands of clients, and how the charts stay at 60fps in Flutter — read How We Built a Real-Time Fintech App with Flutter and Go.