Ask HN: outline for the development of a simple piece of software

Suppose I have an idea for the development of a simple utility -- this could be a program which monitors input from a sensor, processes it, and outputs messages using some communication method, say email.

I know that nowadays there must be many frameworks whereby I can focus on writing the core part of the program in my favourite language, say python, and then once the basic functionality is working, I can throw it in the black box, throw in various user interfaces which the black box requires, and out pops an "app" for download on any platform, a web app, or even an embedded cpu gizmo which functions as a standalone appliance, such as a smoke alarm.

What are some of the best such frameworks, or "full stack toolsets" which are relatively future-proof and popular? In particular, are there any toolsets which accept many languages?

Basically I am asking about the most modern, useful, and fun ways to develop relatively simple programs nowadays and get them out there on several different kinds of platforms.