[Den]

It's basically a group management website/app that has chat capability. You don't have to download anything to access it, and it's super secure. I'm able to access it on my old-ass laptop, and I also have the app on my phone, because my Transformers game alliance uses it to keep in touch, and I'm an officer in the alliance. It's 100% free to use, but you can buy sticker bundles to spice things up.