Kiwi 0.5a is available for Windows, Linux and Mac from my site (click the "WWW" button below).
It is possible that this version is actually weaker than 0.4d, because it is a bit slower and I've had to remove some features in order to simplify the code. Hopefully, it will catch up and improve from the next version.
Thanks a lot to the Winboard Forum folks for their help and support, I've got many good ideas to try in future releases!
