Is there a way to side load apps (appx) on a Windows 8.1 phone? I have built an app but it's not loaded on the windows store yet. I would like to send to a few friends to test out but I can't find a way to load up these apps without Visual Studio.
There is an easier way than what has been desdcribed to you, I own a Microsoft Lumia 435 and I was able to do this with an app I had developed.
Go to Settings → For Developers, and enable the "Sideload Apps" option.
Now you need to plug your Lumia into a USB port on your computer/laptop and copy the .xap file from your computer to your Lumia's SD card.
Unplug from USB port and open Windows Store, then press the "More" option and then press "Install Local Apps".
Now install the app you wanted to install.
Job Done ;)