You can route DDR in KiCad and there are some online reports of people doing that. KiCad is not as nice as the paid software and there are shortcomings but I think 'pretty useable' covers its status accurately.
I wouldn't describe this as a "pretty usable" means, however, for the same reasons KiCad is unusable for DDR routing.
https://www.kicad.org/made-with-kicad/categories/Single-boar...