Question: I read someplace that (I guess for security reasons) the new Windows 10 S will only run programs that are from the Windows Store. I like to write my own programs. Will they not run unless I put them in the Store first? If I give my programs to family and friends, will they likewise not run?

Answer: 
### Will they not run unless I put them in the Store first?

They won't run if you don't put them in the Store. See below.

> 
> If I give my programs to family and friends, will they likewise not run?
> 
> 
> 

They won't run. See below.

> 
> **Which apps and hardware work with Windows 10 S?**
> 
> 
> Windows 10 S works exclusively with compatible apps from the Windows
>  Store. The vast majority of apps available in the Windows Store will
>  work on Windows 10 S the same way they will work on Windows 10 Pro and
>  Windows 10 Home. Note that some developer tools will not be supported
>  for use on Windows 10 S and a small number of apps with known
>  compatibility issues will have notice of the issue included in the
>  app’s product detail page in the Windows Store. 
> 
> 
> **What happens if I need to use an app that is not compatible with Windows 10 S?**
> 
> 
> If you try to use an app that is not available in the Windows Store,
>  you will see a reminder that apps used with Windows 10 S must come
>  from the Windows Store. In some instances, you may also see a
>  suggestion for a category of similar apps or a specific app that is
>  already available in the Windows Store. Note that some developer
>  tools will not be supported for use on Windows 10 S and a small number
>  of apps with known compatibility issues will have notice of the issue
>  included in the app’s product detail page in the Windows Store. 
>  Ultimately, if you want to download an application that is not in the
>  Windows Store or has compatibility issues, you can choose to switch
>  out of Windows 10 S configuration to Windows 10 Pro.
> 
> 
> 

Source [Windows 10 S FAQ](https://support.microsoft.com/en-us/help/4020089/windows-10-s-faq)
I've since found out that Windows 10 S will have a "developer mode". This allows you to develop an app without constantly uploading and downloading it. Once it is finished you'll hae to upload it to Windows Store for other people to use. On the store you can specify that you only want it to be downloadable by certain people. So, apps you develop for yourself (and possibly family members and friends) will be downloadable then.