Maybe it's just the knee-deep affirmations and positivity I wade through when I log into it, but I love Padlet as a bulletin board/whiteboard tool. Padlet is really much more than a whiteboard; it's more a like a Wiki where you can have people share. Or it can be just a bulletin board. Or a multimedia blog or portfolio. Or a chat board.
A free Padlet account just gets you 3 padlets, but you can post as many items of almost any type as you want, as long as each is under 10MB. Something that really adds dimensionality: you or your collaborators can add links to their padlets. Padlet as of this writing offers 8 templates, although that has changed over time. The templates guide the appearance and arrangement of items, but the offerings are broad enough that it doesn't feel restrictive. The Canvas template is the most free form. I like the Shelf option that arranges posts in columns. I find this works well with group activities. I have not used the Map or Timeline templates, but they seem fantastic for activities where time or space is the key dimension.
Padlet has been around for almost 10 years, so there are lots of examples out there, from wedding planning to peer assessment. It's a pretty commonly used app in K-12 instruction. I want to throw this in here: For work collaboration, and typical whiteboard functionality. Microsoft's Whiteboard works nicely in our Spartan365 Suite. The media richness and beauty of Padlet, though, can't be beat!