Microsoft provides official Windows 10 development VMs for:
An online Windows 10 emulator typically refers to a web-based virtual environment that mimics the Windows 10 interface and basic functionality, running directly in a browser. These are not true emulators in the hardware sense (like QEMU or VirtualBox), but rather: windows 10 emulator online
Shells is the industry leader for "browser-based OS." They offer a true Windows 10 virtual machine that you access via a browser. Microsoft provides official Windows 10 development VMs for: