Alongspace has become my new go-to for collaborative work. I love that it integrates seamlessly with HubSpot. With just a click from a HubSpot deal, I can instantly spin up a project workspace for won deals, complete with action plans and automatically assigned tasks (to myself, my clients, or both). Plus, almost anything can be embedded proposals, spreadsheets, checklists and everything stays perfectly on-brand, which I really appreciate. They've also recently added custom domain support, which gives a really polished, professional feel.
The only drawback I’ve experienced is their reluctance to assist with changing registered email addresses (likely tied to the terms of the AppSumo deal). When we upgraded our email from ourbusinessname at Gmail to support at ourbusinessname - even though it was super obvious it was our address, we found it difficult to update within the platform - so it seems we are stuck with the wrong email address on our support contact links so we have to create this without using the default "welcome section". It's a minor hiccup, but worth noting if your business email might change down the track.

----**UPDATE** - In my package I can invite a team member with the correct contact email and ph... and if the space is created by that team member then my contact info and notifications issue is resolved.