I spent some time working on these, so I thought I'd share.
KSP Serial IO Debug Tool - A fork of the original tool, but updated for the current version. Source only. May extend to properly send/receive SAS Mode, but I just wanted something that didn't require restarting KSP all the time...
KSP Controller Arduino Code - Modified to use 74LS595 Shift registers to handle I/O (yes, I know there are better input solutions, but it's what I have). WIP, need to add stage and abort locking logic as well as LCD support.
Edit: I ended up turning off the CRC check to avoid connection issues.
https://github.com/madlemur/KSPSerialIODebugTool/releases