Past Projects and Testimonials

Project gallery

Secure payments

Global payment service provider

An expert from HappiHacking was assigned as appointed expert advisor for Klarna's core system and for system development in Erlang. The tasks included areas such as system development, architecture, monitoring and product development. Thanks to our help and expertise, the customer was able to stabilize their most vital system and thus meet the demands of increased traffic and demands from their customers.

Related blog posts:

The Birth of Kappa

Just in Time Development

Innovative data streaming

Deutsche Telekom

We were chosen to help DT designing and implementing new IoT services for their customers. We delivered an architecture and proof-of-concept solution for high volume data gathering and analysis, handling billions of messages per day.

“If you are searching for a motivated team that will go the last mile with you, deliver qualitative stuff and understand bad jokes…Happihacking is the right choice!”

Filiz Hazer-Yilmaz, Deutsche Telekom

Related blog posts:

Rapid Protoyping

Global block chain


æternity is a major European blockchain project, see As part of the core team, we designed and developed a new blockchain in Erlang. We also implemented, among other things, FATE, a virtual machine for the programming language Sophia (used for smart contracts), block validation and Merkle trees for state management. Thanks to our engagement and competence, the core team delivered successfully all milestones in a timely fashion and with top level quality.

"HappiHacking provides solid engineering even in the most risky projects!"

Michał Zajda, CEO Sennui Lab

Related blog posts:


Audits through Merkle Root Hashes

Complex video chat service

Deutsche Telekom

HappiHacking helped DT design and implement a new video chat service for the home. We delivered an architecture and a solution for a high-quality video chat service with dedicated hardware and co-watching of movies or TV while video chatting with emojis.

Related blog posts:

Rapid Protoyping

Book about the BEAM

The BEAM Book

Erik Stenman (Happi) is the author of The BEAM Book, which is available for free online.

"Recent discussion reminded me about this great book on lower-level working of ERTS/BEAM by @erik_stenman. Highly recommended, I think I'll reread it myself :-)"

Saša Jurić @sasajuric

Related blog posts:

The Power of Erlang's BEAM

HappiHacking's New Course on BEAM

Mobile Puzzle Game


HappiHacking built a mobile puzzle game: Taba.

Built using Flutter on the front end and Erlang in the back end. See or get the game on your mobile from your store.

“My new favorite game, it is SUPER FUN and addictive!!!”

User on AppStore

Related blog posts:

Taba the Story

Communications platform


“Impressive! This firm dug into our tech and got started fast! Their work was excellent and more importantly, diligent! They stood behind their work and took ownership! I give them 5 stars for sure!!! ”

JR Guerrieri, founder

Erlang language development


HappiHacking helped WhatsApp to investigate new language features and ideas for a typed Erlang.

Top level management


Prior to HappiHacking Erik managed the scaling of the IT department of Klarna from 1 to 80 people. Led the development and operation of a 24/7 internet scale payment system. Scaled the performance of Klarna’s business system with the exponentially increasing business needs of Klarna. As CTO Erik participated in the C-level management together with the three founders of Klarna.

"Erik Stenman was the first CTO of Klarna and, without a doubt, one of very few key people behind its great success. During Klarnas early years Eriks ability to transform C-level Management requirements in to comprehensive and strategic development tasks as well as being a part of the development team that performed those tasks was an invaluable asset for Klarna. As Klarna grew Erik, very smoothly, grew with the company and his responsibilities, handling people and larger strategic issues with the same professionalism and positive attitude as ever."

Peter Elasyeh Head of Development Klarna AB

Happi, also mentored some of the CTOs/CIOs that came after him.

"I really enjoyed our lunches during the year, you helped me a lot whether you realized it or not :)"

Yuval Samet, Chief Information Officer

Related blog posts:

The Birth of Kappa

Just in Time Development

Interim CTO

Travel SaaS

Architecture and team building for German travel packaging system.

“We were able to convince Erik to join our SaaS start-up as interim CTO in a critical MVP development phase. His track record speaks for itself, but what we found most appealing was his humble attitude and pragmatic approach in dealing with us (the company founders) as well as our board.

Erik and his team went to great lengths when it came to developing our target architecture after reviewing our initial plan thoroughly. While we as founders talked a lot about product vision and target picture, he grasped quickly that we were missing a proper technical roadmap and took initiative immediately.

Over time, Erik became more operational and worked closely with our Head of Engineering as well as engineers ensuring they would deliver consistent hiqh-quality output. At this stage, we started feeling confident that we can actually deliver our SaaS solution to the first set of clients. Erik further interviewed most of our hires himself, helping us to form a reliable and motivated engineering team.

Eventually, and also thanks to Erik's contribution, our company was acquired by a strategic buyer after only 18 months mainly due to our innovative technology.”

Marco Krebs, Founder

Technical Advisor

Healthcare Payments

Architecture and team building for the US health payment system.

“Erik supported my company Sika Health in early days as a Technical Advisor. His background having lead and scaled technical teams at Klarna was a distinguishing factor since our business in the health payments space has many elements in common with the Klarna product. He helped me develop an initial technology roadmap so that I could understand who I needed to bring onto my Engineering team to deliver on this roadmap.

Additionally, he’s been a trusted advisor to me personally as a first-time founder/CEO building in fintech. I’ve been able to talk with him about a variety of topics as I’ve built the foundation for growth in my business. I would highly recommend Happi to any early stage founders and executives building in tech who need a thoughtful, warm, and experienced executive advisor to help them start or grow their business.”

Ami Kumordzie, Founder/CEO

Accelerate your project by giving us a call today!

Happi Hacking AB
Munkbrogatan 2, 5 tr
111 27 Stockholm