Home servers can be really handy for streaming media, securing public Wi-Fi, or sharing files between friends. But if you don't have a spare computer lying around to turn into a server, free app Servers Ultimate can do it to an old Android phone.
Servers Ultimate has a bunch of different types of servers built in, such as:
A DLNA or UPnP media server, perfect for streaming videos from your phone to another device
A proxy server for securing and encrypting your traffic on-the-go
An FTP, WebDAV or web server for storing and sharing files
A home DNS server, SMS gateway, Email server, and lots more for you web developers out there
If you wanted more space than your 32GB SD card can provide, you can hook up an external drive to most phones via USB and use that as your main data storage. The app is definitely geared more toward developers than the average user, but it can be handy if all you want to do is share a few files or run a proxy server at home without keeping your computer on 24/7. An old Android phone is small, low powered, and perfect for hiding in the closet. For more ideas, check out Servers Ultimate's Google Play entry below, or check out this thread on the XDA Developers forums.
Servers Ultimate is a free download for Android devices.
Servers Ultimate | Google Play via XDA Developers