Install GApps without flash it I know we can download it in a zip format in order to flash in recovery mode, for exemple from opengapps project. 
What are others solution to install GApps on any android device without to flash? 
Edit : without root and without flash 

GApps : Google applications + Google play services and framework
If you want to install without modifying /system then it's impossible. So the answer is "No, you can't" with neither root access nor recovery flashing. But if you simply wany to DIY without using a custom recovery, it's OK.
Takine OpenGApps as example. Download their ZIP and extract it.  


Install BusyBox  
Use busybox lunzip to extract the .tar.lz files in Core/  
Move files other than APKs to /system. You will find things to be merges into etc/ and framework/. Take care of file mode (permissions) and owner/group.  
Install GoogleServicesFramework.apk as system app. In my experiments it sometimes fail if not installed as system app.  
Install the rest of the APKs as normal.  


You can't install GApps without modifying /system. As you see, there are quite a few configuration files that will be merged into /system/etc during installation, and a few essential framework JARs to be installed to '/system/framework. They won't work if installed elsewhere.