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4xxi is a web and mobile development company headquartered in London, UK with satellite offices in Saint Petersburg and Saransk, Russia. 4xxi's team of 50+ employees provides web development, mobile app development, and custom software development services to startups, mid-market businesses, and enterprises alike. They also have a diverse industry presence, working with healthcare, financial services, and education firms. 

Client Insights

Industry Expertise

Financial services






Business services


Consumer products & services


Information technology


Other industries


Client Size Distribution

Small Business (<$10M) 40%

Midmarket ($10M - $1B) 40%

Enterprise (>$1B) 20%

Common Project Size

$50K-$199K 4 projects

$200K-$999K 3 projects

$10K-$49K 2 projects


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Highlights from Recent Projects

Overall Rating

13 Reviews

4xxi was hired by Challenge Social, a social platform, to redevelop their mobile application and website. The previous development company had failed to deliver a satisfactory platform, leading to the need for a complete overhaul. 4xxi was selected for the project due to their strong recommendations and trustworthiness. They created a native iOS and Android app that was scalable and high-quality. The project involved a complete redesign and recoding from the ground up. The team consisted of backend and iOS and Android developers, a QA, a BA, and a project manager. The client was highly satisfied with the work and plans to continue working with 4xxi in the future.

The owner of an auditing firm hired 4xxi to develop a platform for auditors and audit companies. The client had no development resources and needed to build the entire infrastructure based on their ideas. 4xxi was selected because they provided a clear budget plan, scope of work, and schedule. They handled design and programming, providing all the documentation and code. The team was made up of five to six people, including a product manager who was in constant touch with the client. The project was completed within four months and the client was very satisfied with the results.

Virool, a video advertising and branding firm, hired 4xxi to assist with the development of their platform. The internal engineering team was overwhelmed by the project's scope and needed a reliable partner. The goal was to create a user interface for their advertising platform that was easy to support. 4xxi was selected because they offered the best terms. They worked on the UI elements of the customer analytics dashboard for the advertising platform, eventually taking over the entire dashboard. The team consisted of a project manager, a QA specialist, and three engineers. They used an agile methodology to keep the team aligned and autonomous. The client was highly satisfied with the work and appreciated the team's ability to adapt to changing demands.



Service Excellence




Would Recommend