Sublime Text 3
The lightweight and very popular text editor supports a lot of programming languages. You can use a free version or buy a license for 80$. I think it’s a must to have editor and successfully replacing Notapad++. Responsiveness and speed is a very big advantage when you have limited ram/cpu. If out of box functionality is not for enough you can search and install packages
Visual Code
Created by Microsoft, Open Source free IDE, VS Code supports many programming languages and is lightweight enough to work on slow computers. It’s one of the best editors for JavaScript/Typescript but you will need to install extension to make it work well with PHP.
Netbeans
Created by Apache Software Foundation it’s free and open-sourced. Great out of box PHP support, greate autocomplete function, for professional PHP programmer it should be great IDE but uses a lot of resources, it can be slow and not very responsive on a slow computer.
PHPStorm
Costs 199$ the first year and also have free trails for 30 days. Considered as BEST PHP ide! It’s heavier then VS Code & sublime but it’s much more powerful than any other in this list. No matter on which PHP project you work, it feels like Phpstorm just understands your project and helping you to do things much faster. The only downside is price but if you can afford it, it’s best.