Ssh server. File transfers with protocol SCP and SFTP are available. Command line is also available (beta version). Command line needs "/system/bin/sh" preinstalled.

Intents:
com.theolivetree.sshserver.StartSshServer
com.theolivetree.sshserver.StopSshServer

To start the server automatically use application "Autostart and StaY!"
https://play.google.com/store/apps/details?id=com.atasoglou.autostartandstay
or also Tasker with the intents provided.

I have tested the server using:

*Secure file transfer:
WinSCP : http://winscp.net/
FileZilla : https://filezilla-project.org/

*Command line:
Putty : http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html