Tried SIO Server the other day and while it ostensibly works fine with my FTDI interface, it has serious problems with double-density disks and keeps timing out. Single-density ATRs seem to boot without issue, which I find quite strange. I'd like to know what's going on with that. If SIO Server also did folder imaging (and I could iron out the transmission problems), it would be a really nice alternative.
I really don't want to hijack this AspeQt thread, but I will post a few bits to contribute to the turn the conversation has taken.
I wrote SIO Server to scratch an itch I had a few years ago. It was designed to satisfy my own personal requirements, and then I released it to the public just in case others might derive some utility from it.
Until recently, SIO Server has had two active users that I know of. The double-density bug is definitely in there (and fixable), but I never did get around to correcting it because it wasn't a problem for my personal use-case and there were other peripheral emulator solutions that everyone seemed pretty happy with.
SIO Server is actually two programs: the GUI process and the communication daemon. When the GUI launches, it spawns a priority-elevated communication daemon as a child process. The daemon and the GUI communicate with one another using piped I/O. The approach minimizes CPU usage and helps to ensure that the priority-elevated daemon can continue to communicate even if the host system is delayed updating the GUI.
Although I am a long-time Mac OS X (née NEXTSTEP)/iOS developer, the GUI is written in Java in order to facilitate porting the app to other POSIX-compliant OSes. The core of the communication daemon was written in portable, POSIX-compliant C by Belboz, and I added many enhancements to it. The communication daemon has been tested on Mac OS X and Linux systems, and it can be launched from the command line.
In short, I never got around to fixing the double-density issue or to creating a Linux build because: I was happy with the software (for what I needed), nobody else was terribly interested, and I've had little time to spare anyway. That said, I am glad to see that the program has proven helpful in some way: as a troubleshooting tool.