[skibz]

My tool of choice for this is LightBlue. It's not fully cross platform, unfortunately, but it works great on Apple devices. (https://apps.apple.com/us/app/lightblue/id557428110)

I've also dabbled with bleno and noble for emulating and/or communicating with peripheral and central devices, respectively. (https://www.npmjs.com/package/@abandonware/bleno)