I've never used it TBH, so I don't know, but productivity tools in general are well-tread ground. There's a bunch of open source options. I understand how a company can make a profit by providing such software as a service, but having an IPO at the valuations they did seemed so bizarre to me. Or that a VC would fund something like that in the first place.

I use plain text files for planning, but maybe I am not planning complex enough stuff, who knows...