Basecamp. Their product is designed to make long-form written communications enjoyable/easy. I even wrote a blog post about what they have to say: https://blog.pixelic.io/jason-fried/
But I hear you - I founded a remote startup as well and at times we have lengthy discussions and it's difficult to do them remotely. BTW, are you building a digital product? If so, I'd love to talk to you, we're building a tool for software development teams. Let me know if you're interested in doing a 10-15 min call to exchange notes. chris at pixelic.io. Thanks!
We use Trello and GDocs (slack only for shallow stuff). Curious how Basecamp is different in terms of discussion threads. trello seems fine, but something is a bit weird when discussions are deeper or longer. I can’t exactly put my finger on it, that’s why I wonder how it compares to Basecamp
