Does Microsoft Carioca Rummy run on Windows 10 and is it still free to download for Windows users?
No, the software won't work on Windows 10, because Microsoft doesn't support it. The latest version of Windows supported by Microsoft Carioca Rummy is Windows XP. You need a virtual machine running Windows XP in order to play the game.
Luckily, there are other games you can play instead considered as alternatives: http://software.informer.com/search/rummy
If you want to take the hard path, then Virtualbox is the solution required for virtualization: https://www.virtualbox.org/wiki/Downloads