> Lotus Notes was underrated imo.

For what it was, yes.

For what a great many people used it for on the other hand…

It was a great platform for making document and workflow control applications, and was ahead of its time in terms of a proper PKI system for authentication/access/verification and access control lists and such. But many people hit a poorly made application and that coloured their opinion for the rest, and in the list of terrible applications I'm including the standard email support, which was a royal PITA, and most custom versions for that function. The general UX wasn't great either, not so bad that you couldn't put up with it for a great application but if you are hating the rest of the application then the general UX issues grind your gears too.