ACP Commander is a Java-based tool developed by a nas-central.org user called georg in 2007. This utility uses the same protocol used by Buffalo's management utilities to perform administrative tasks to run commands and perform useful tasks like enabling root access over telnet. In recent years a few of us have forked the original code and have made some adjustments which allow it to work on newer devices as well as some new features and bug fixes.
Current source code and binaries can be found at:
Several years ago someone made a GUI front end for ACP Commander with many common tasks available as one-click buttons. It hasn't been updated since 2012 or earlier and the site which hosted it was eventually decommissioned. It also didn't include any source code or license information which prevented it from being updated like the command line versions.
Some of its features involve making edits to system configuration files on the device which can cause harm if used with some devices. Although it still mostly works for many devices I strongly recommend using the actively maintained command line ACP Commander instead.
The Internet Archive still has copies available for reference: