Mobile App Development for iOS, Android & .NET

I’m Justin Sinnard, a senior full-stack mobile developer specializing in iOS (SwiftUI), Android (Jetpack Compose), and .NET / Azure backends. Sinnard Technologies focuses first on mobile app development, while also building websites, desktop applications, Apple desktop apps, backend systems, and UI/UX design for small businesses, creators, and startups that need real, production-ready software.

Schedule a Call View Services

Available for custom software projects and contract work. Remote or local (Wisconsin / Oshkosh area), serving Fox Valley businesses and nationwide clients.

Featured Project: PumpPal

Cross-platform fitness app built with SwiftUI, Jetpack Compose, and a .NET backend on Azure. Includes plans, workouts, progress photos, measurements, subscriptions, and full error handling.

  • iOS & Android native apps
  • Secure authentication & token refresh
  • Azure API + SQL database
  • In-app purchases & ads
Mobile app design showcase

What I Do

Mobile App Development

Custom iOS and Android apps built with modern tech: SwiftUI and Jetpack Compose. Perfect for small businesses, gyms, creators, and startups that need more than a website.

Websites & Desktop Applications

Business websites, internal tools, desktop apps, and Apple desktop apps that support your operations and give customers a polished digital experience across more than mobile.

Backend APIs & Cloud Systems

.NET / C# APIs, Azure hosting, SQL databases, authentication systems, background jobs, and cloud-connected backend services that power mobile apps and broader software platforms.

Website design showcase

UI/UX Design & App Validation

UI/UX Design Services

Interface design, user flows, and product thinking for mobile apps, websites, and software products that need a clearer user experience before development starts.

Mobile App Validation Plan

A structured validation option for local businesses and founders who want to test customer demand before committing to a full mobile app build.

Looking for a Local App Developer?

If you’re searching for a mobile app developer near you in Wisconsin or the Oshkosh area, I build custom apps, websites, and software for small businesses: landscaping, fitness, retail, restaurants, service companies, and more.

Tell Me About Your Project