I'm browsing through my mobile phone and I need to download unity assets but unity asset store demands that I open the assets in unity directly. How or which site can I download it on my mobile and send it to my PC.
It isn't possible to do it outside of Unity3D. However, you could write a script that can pull the data from URLs of your choice in a Unity project and save it to a specific folder on your computer, that way you have the assets for later. Or, you could just have a dummy project and download all the assets that look useful for your current and possibly future projects as a means of storage for later use. This isn't exactly what you want, but as far as I know, these are the only ways you could do it.