Denis Hennessy, Software Developer in Greystones, Ireland
Denis Hennessy

Software Developer in Greystones, Ireland

Member since November 4, 2020
Denis is a passionate engineer who loves building products that people actually use. In particular, he's been building iOS apps since the first iPhone launched. He has a high level of expertise in Swift and Objective-C. Since a modern iOS app is rarely a standalone entity, he's also worked with many external frameworks, including building REST endpoints where SDKs didn't already exist. He's also got experience building large server products, as well as some embedded-systems work.
Denis is now available for hire




Greystones, Ireland



Preferred Environment

Xcode, MacOS

The most amazing... I've developed is an app that helps people suffering from bipolar disorder to understand their symptoms by recording their mood each day.


  • Principal Developer

    2007 - PRESENT
    Peer Assembly
    • Developed a medicine dose tracking app for a pharmaceutical company that provided consumers of the drug an easy to use way to track their usage while providing a significant market advantage for the company.
    • Built a language-learning app for teaching Hebrew to children. I managed all phases of the project from requirements capture, development, testing, and successful launch.
    • Developed a mobile game for a US fast-food chain. Besides being fun to play, the game also was an important part of their customer loyalty program.
    Technologies: Objective-C, Swift
  • Principal iOS Developer

    2018 - 2020
    Major US Media Company
    • Converted a large portfolio of apps from an ad-supported revenue strategy to a subscription-based offering.
    • Managed a major project evolution from a primarily Objective-C codebase to a primarily Swift codebase, while significantly enhancing the app feature set.
    • Established a continuous-integration system to handle the quality assurance and automated release process.
    Technologies: REST, Core Data, Swift, Objective-C
  • Principal iOS Developer

    2016 - 2018
    Makalu Inc
    • Took over development of their iOS location bookmarking app, updating it with the latest iOS platform features and adding new photo capabilities.
    • Developed the "event app" for a major annual rock concert under demanding schedule constraints.
    • Developed an educational app which encouraged children to write letters to elected officials.
    Technologies: Core Location, Core Data, Swift, Objective-C
  • Principal iOS Developer

    2014 - 2016
    Time Marketing
    • Developed an innovative wine tasting and cataloging app for serious wine enthusiasts.
    • Worked with the project owner and external design freelancer to come up with a unique look and feature set.
    • Managed the evolution of the app from a paid-up-front model to a free-with-IAP model.
    Technologies: Core Data, Swift, Objective-C
  • CTO and Co-founder

    1999 - 2007
    Valista Inc
    • Handled the architecture of Valista's range of telco-grade payment and messaging products.
    • Managed a distributed development team with centers in Ireland, Sri Lanka, and California.
    • Set up a continuous integration system to improve the quality of software releases and increase the pace of updates.
    Technologies: Ruby, Java, C++, C


  • Goal Streaks

    Goal Streaks helps you achieve your goals by tracking your daily progress and encouraging you to stick with it for longer and longer streaks. The idea of maintaining a continuous streak is a great motivator to help users stick to a project when they might otherwise quit.

  • Focus Time

    Focus Time is an app that helps you practice the Pomodoro Technique—a way of achieving distraction-free work by alternating periods of intense focus, and short breaks to clear your head. I originally wrote the app in 2012.

  • Rego - Bookmark Your Places

    Rego is an app that lets you easily save "bookmarks" for places you've visited, and attach photos and other data. People use it to save favorite tourist spots, restaurants, and even parking places. The app was originally an upfront payment app and is now free-with-IAP.


  • Languages

    Swift, Objective-C, Python, Ruby, C, C++, Java
  • Frameworks

    iOS SDK, SwiftUI, Core Data
  • Tools

  • Paradigms

  • Platforms

    MacOS, Linux, iOS, Firebase
  • Storage

    SQLite, PostgreSQL
  • Other

    Software Development

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