I am currently the (only active) maintainer of knxd.
To talk to KNX, you need
Hardware is simple, install a KNX/IP or KNX/UDP gateway. Software is simple too, you instell eibd.
Umm … not really.
An IP gateway is nonsense, it costs €150 and you already have a Raspberry Pi in there. A commercial USB gateway is also nonsense because the ETS programmers didn't want to deal with writing an USB driver, so they bolted KNX on top of the HID (Human Interface Device) specification, which KNX is kind of … not. This has been proben to be unstable, long-term.
Which leaves us with the software problem. eibd hasn't been maintained properly for years and didn't work with ETS 5, thus a couple of people forked it early in 2015. I mentioned in passing that I'd like to help … and 50 commits later I'm the person with the "knxd maintainer" hat.
Oh well. Somebody's gotta do it. 😎