PowerDVD is the software you'll find included with most blu ray drives. It will be a slightly crippled version compared to their retail software. The version that came with my LG drive would only output in 2 channel stereo, rather than support the HD audio.
I prefer Arcsoft TotalMedia Theater, but it is rarely bundled with drives, and if you buy it at retail, it now costs more than some blu ray burners.
It is possible to play an individual m2ts file from the Streams folder within blu ray structure. Most blu ray movies will have the main movie contained in one of these m2ts files, but some are split across several files. So this makes playing them back a bit problematic when using free software. But it is possible to use something like Media Player Classic HomeCinema with m2ts files. You won't get the menus, which makes playing extras difficult. MPCH is about as close as it gets for free playback of blu ray.