Companies using Flutter in mobile development
MongoDB
HQ: United States Golang, Python, Dart... TypeScript Docker, Kubernetes MongoDB️ AWS, Azure, GCP...
Netguru
HQ: Poland Python, Node.js, Ruby... JavaScript, React, Angular... Ansible, Chef, Docker... ️ Azure, AWS, GCP...
Python 
Front-end 📊 Product/Management
JVM ☁️ DevOps
JavaScript BE 
Golang 🎨 UI/UX Design
📱 Mobile
PHP 
C#/.NET 
Ruby/RoR 🔨 Testing/QA