Dan GillmorThe best thing Yahoo ever did was called Pipes, and needless to say the company starved and then killed it.
Read this superb history by @glennf to understand what we had, and lost.
Grassroots JoeDid you ever run into Groove Networks?
It was a great team environment in the mid to late 90s that allowed real-time remote collaboration as well as offline updating that synced across the team as soon as you got back online.
The WAN implementation also met DOD security requirements.
If memory serves, Microsoft bought it, killed it and stripped the parts to use to start building Teams which still sucks in comparison (except video; insufficient bandwidth back then).