Application for all OS?

Question

Mobile development

I need an application, I want to write it myself, because I have absolutely no money, I used to work only with php, js and similar "simple" languages.
You need an application something like "Vkontakte"
as well as working with api ..
Learning different languages ​​\u200b\u200bto create 1 application is somehow stupid, I read somewhere about creating a multi-platform application
What do you say, is it difficult?
Throw someone who has some MB articles, thanks to everyone)

Answer 1

https://xamarin.com/
ps
IMHO, bad idea.

Answer 2

Do
I allow

Answer 3

Will it be on Brew?