TinyCA is not available for Windows but there are a few alternatives that runs on Windows with similar functionality. The best Windows alternative is xca - X Certificate and Key management, which is both free and Open Source. If that doesn't suit you, our users have ranked five alternatives to TinyCA and four of them are available for Windows so hopefully you can find a suitable replacement. Other interesting Windows alternatives to TinyCA are KeyStore Explorer (Free, Open Source), SimpleAuthority (Freemium) and Certificate Management App (Free).
X Certificate and Key management is an interface for managing asymetric keys like RSA or DSA. It is intended as a small CA for creation and signing certificates. It uses the OpenSSL library for the cryptographic operations.
xca - X Certificate and Key management vs TinyCA opinions
Most users think xca - X Certificate and Key management is a great alternative to TinyCA.
I has all needed functions, the missing one is a webinterface
KeyStore Explorer is a free GUI replacement for the Java command-line utilities keytool, jarsigner and jadtool. KeyStore Explorer presents their functionality, and more, via an intuitive graphical user interface.