Ruby on Rails
Our mainstream option for rapid prototyping, used very successfully by companies such as Airbnb, Twitter to reach a significant user base quickly. An enourmous community and rich ecosystem allows for quickly building pretty much any kind of web-based system.
We know it like the back of our hands — and we know it takes extensive experience and discipline like ours to achieve good maintainability and scalability. However, it becomes much more useful combined with GraphQL for web APIs.
These days, it is our technology of choice for open-source platforms, due to it being well-known by most of the developer community.
We also used very successfully in one of our main products, Empresaula, to empower vocational training students with business administration skills.