This strongly depends on the purpose... How is it sized? Can it get bigger? Is it realtime? Is it Web / App / Other frontend? What backend languages

This strongly depends on the purpose... How is it sized? Can it get bigger? Is it realtime? Is it Web / App / Other frontend? What backend languages / tech is supported? I always wanted to try or tried successfully: SignalR (C#) Flask (Python) Gorilla (Golang) Revel (Golang) API Platform (PHP) Hapi (js) Express (js) Actix-web (rust)