Question: I have a quick question.

Here is the scenario.
A friend of mine owns tennis courts.
He needed a system where he could reserve courts for customers and cancel reservations (not the customers to reserve, but himself. Just for him)
Basically, I made a react project.

I have finished the project and it works perfectly fine.
It has got the front end, server and database postgreSQL (ph Admin4).

My quistion is:
Is it possible to use the project without getting a website?
Basically just use it in the phone without purchasing domain and hosting.

Answer: 
Free Frontend App Hosting Solutions
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You can use free hosting solutions to deploy your front-end application.

The most known ones are:

* Vercel
* Heroku
* Netlify
* GitHub pages (With GitHub actions, to build React projects)

I personally love **Vercel**, I think it is the easiest one, pretty straight forward, and it creates URLs like:

`your-unique-project-name.vercel.app`

It lets you connect to your GitHub repo, then once you commit it automatically deploys the app, and you can register a custom domain if you decide to buy one afterwards.
It's possible. Get a dedicated computer, run the app such that it's available on localhost (for example, such that typing http://localhost:8080 into the address bar comes up with the React interface - this is easy to do, many boilerplate React projects have this sort of thing set up automatically for live testing). Then either use the computer to interact with your reservation system, or connect the computer to a router and then use another device connected to the same router (whether a phone or another computer) to access the dedicated computer.

For example, if you can use

http://localhost:8080

on the dedicated computer, you could configure the router such that said computer gets assigned an internal IP of 192.168.2.0, allowing you to access the app on the other device by going to

<http://192.168.2.0:8080>

But there are free hosting services available (like Heroku) - you might look into those too, you may not have to spend any money anyway.