Torch is a scientific computing framework with wide support for machine learning algorithms. It is easy to use and efficient, thanks to an easy and fast scripting language, LuaJIT, and an underlying C/CUDA implementation.
Is there a way to install torch on MS Windows 8.1?
I got it installed and running on Windows (although not 8.1, but I don't expect the process to be different) following instructions in this repository; it's now deprecated, but wasn't deprecated few months ago when I built it. The new instructions point to torch/torch7 repository, but it has a different structure and I haven't been able to build it on Windows yet.
There are instructions on how to install Torch7 from luarocks, but you may run into issues on windows as well; I haven't tried this process. It seems like there is no official support for Windows yet, but some work is being done by contributors (there is a link to a pull request in that thread).
Based on my experience, compiling that deprecated repo may be your best option on Windows at the moment.
Update (7/9/2015): I've recently submitted several changes that fix compilation issues with mingw, so you may try the most recent version of torch7 and follow the build instructions in the ticket. Note that the changes only apply to the core lib and additional libraries may need similar changes.