Old samsung phones other operating systems?

I have a number of old samsung phones..s1 s2 s3 s4 note2 etc

Any one developing anything to make use of them?
Like make one into something like a raspberry pi like device?
Maybe install raspbian on it as the primary os
They are both arm7 right?
Servers for files, personal email/own cloud server.
Local Wi-Fi ftp, backup, sync system..


Anything like that..
I hate not making better use of them