Roblox is not an appropriate tool for making an operating system that competes with operating systems that’s made by a large cooperation that (probably) has like over thousands (or millions) of engineers behind it (Windows and macOS).
Also this is not a trivial thing to do, especially if you want it to compete with the operating system you mentioned.
Please, like many other said, use a system language for this, not a 3D game engine that’s designed for creating 3D experiences that requires internet connection and an online account.
How would you modify it exactly? How would you open Roblox (technically)?
If you actually want to compete with other operating systems; I have to ask, why are you using a 3D game engine on a sand-boxed environment for this?
What field do you want to compete the two operating system in? Why should we use your operating system over Windows and macOS? What does this offer that others don’t?
I guess you could use the HTTPService in combination with the rich text option on labels to have some very basic html-like formatting commands. Unfortunately there are no links so you’d need to deal with that somehow and obviously images and other media-files aren’t possible to use since they need to be uploaded through roblox.
I use exactly that for displaying update-news and announcements in my game.
I mean by how would you do it by modifying the source code (which isn’t really needed) to do this as he said to modify it, I assumed meant by modifying the source code.
…and based of this post
I guess he would have to create an account for this a lot of times for someone else and for profit, and I guess that would violate the TOS.
Ok, I guess I’ll have to learn more about computers to figure out a way that this will work. I still like the roblox game idea though even if it’s not it’s own computer!