The TTTTT main body assembly was drawn in FreeCAD and I then used the LC interlocking workbench to automatically add the tabs and slots to fit it together. I've been learning about this addon workbench and made a short video about it's use here.
Having used the tools to generate the tabs and to flatten the design into a single plane, I then used the Path Workbench to set up toolpaths to cut the main parts of the TTTTT. I also used the dog bone dress up tool in FreeCAD to add small extra cuts to make sure the internal corners of the pieces didn't contain a radius left by the tool. The TTTT is assembled from 3.1mm plywood and I cut all the pieces with a 1.5mm endmill... as it's what was in my CNC router at the time and I'm lazy. :)