FTPDroid

FTPDroid is an FTP server for Android that will let you to manage files and folders on your device without the USB cable.
The benefits of using this application are:
- Transfer files and folders to/from any computer and your device without the need of the USB cable.
- No need anymore to mount/unmount the SD card.
- Easily share files with other devices (Android or anything else, see the FAQs)
- Keep the USB port of your device safe.

Why FTPDroid is the best FTP server for Android? Because it's not YAFS (Yet Another FTP Server) since is a native port to Android of best FTP server around: Pure-FTPd http://www.pureftpd.org

Features:
- Anonymous access
- Configurable users
- Restrict access to specific folders
- Active and passive mode
- Multiple files transfers
- UTF-8 support
- Root support to allow binding on standard FTP port 21 (please note that root is supported but NOT required)
- SSL/TLS support (pro)
- App widget (pro)

FAQs:
q: How can I share files with another device?
a: Look for an FTP client (every system like Android, iOS and Windows Phone has its own).

q: Why my transfer speed decrease when I turn off the screen?
a: Enable the option 'Lock Wifi'. If your device is running at least Android 2.3.x, you should get full speed transfer even when the screen is off, otherwise enable the option 'Lock screen' too.

q: How can I disable anonymous access?
a: Please follow the instructions in the help (open the menu from the main page of the application).