Is there any free windows software that can play 3D Blu-rays?
No, not yet.
The issue is that in order to read commercial blu-ray disks (which I'm assuming is what you're after, that being playing 3D movies), you need a codec that is capable of decrypting the blu-ray disk. In the US and many other countries, licensing the decryption keys from the Blu-ray Disk Association requires money, and a good bit of it-- to make up these costs, all companies which are marketing Blu-ray players and playback software are selling them instead of making them available for free download. Moreover, it is a legal grey area (in the US and some other countries) to reverse engineer or otherwise circumvent the encryption (It's DRM, and falls under DCMA), so even if someone wrote a library that did such, any media players using it would make themselves into high-profile targets for lawsuits and harassment. The encryption used on DVDs had the same issues (which is why Linux took so long to get proper DVD playback), and the library used (libdecss) is used widely now only because software authors feel rather confident that the the DVD consortium will not chase after them and has more or less given up on securing that format.
The internal video formats used for Blu-ray disks however are well-known and mostly supported, and if you use a product such as SlySoft's AnyDVD HD, which will transparently decrypt the disk and provide applications with access to the decrypted movie files, then players such as MPlayer, VLC, and others might be able to play back the disk by manually browsing the video files on the disk and playing them.
It's worth noting that the free players also lack many of blu-ray's features at this time beyond straight video playback, such as proper menu support, BD-J, and BD-Live. I imagine these will come with time, but I would not expect them to be working within the next several months. VLC is expected to add playback for encrypted bluray disks with version 1.2, and is all around a very good video player. I'd keep an eye on that one if you want one to watch the progress of bluray support.