Hey there, super sorry for the late reply! I wasn't checking itch.io because of the Thanksgiving break.
NW.js is an open-source project that allows people to turn web apps like WriteRush (made with Javascript, HTML, and CSS) into desktop apps. I use Web2Executable (which uses NW.js) to convert them into desktop apps. You can find that here. NW.js is trusted and safe; it has almost 40K stars on github.
NW.js is not malicious. It's a tool used to create programs. Someone must have used it to create a virus, which is why viruses show when you look it up.
It's safe to run. But if you're still wary of it, you can use the web version, which doesn't use NW.js.
Also, I don't have a mac to test the mac version, but `nwjs.app` should run WriteRush on mac.
Hope this helps, and if you have any more questions, ask me!