TJFileTransfer allows you to transfer files onto your iPhone using iTunes File Transfer and web sharing. It essentially converts your iPhone into a removable storage without installing any additional softwares on your computer. For the convenience preview is also supported on selected file types so you can view them without copying it onto your computer first.

How to use this app:
Install the app onto your iPhone
Launch iTunes
Connect your iPhone to the computer
Make sure the computer is trusted on the iPhone
Select the iPhone in iTunes
Under apps menu of your iPhone (file transfer for iTunes 12.7),
select TJFileTransfer
Drag files you want to store into the files list to copy onto iPhone

Notes:
Applications (.app) copied into this app will not open anyone when restored to another computer. Workaround: Zip the app before copying.