Termux is not available for Windows but there are a few alternatives that runs on Windows with similar functionality. The best Windows alternative is Cygwin, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to Termux and four of them are available for Windows so hopefully you can find a suitable replacement. Other interesting Windows alternatives to Termux are MinGW (Free, Open Source), MSYS2 (Free, Open Source) and PentestBox (Free).
Cygwin is a Unix-like environment and command-line interface for Microsoft Windows. Cygwin provides native integration of Windows-based applications, data, and other system resources with applications, software tools, and data of the Unix-like environment.
Cygwin vs Termux opinions
Almost everyone thinks Cygwin is a great alternative to Termux.
PentestBox is an Opensource PreConfigured Portable Penetration Testing Environment for the Windows Operating System that allows users to use it without any virtual machine. It has got maximum of Kali Linux tools in it. And it requires very less space.