These tools are taking a new approach to the problem, which is to constantly monitor for encrypted files and stop the relevant processes, thus often limiting the loss to the first few files. Some have proved far more efficient than any standard antivirus as of now:Linux, Windows:
https://github.com/unixist/cryptostalker
OSX:
https://objective-see.com/products/ransomwhere.html
more theoretical information on Cryptodrop's paper:
http://www.cise.ufl.edu/~traynor/papers/scaife-icdcs16.pdf