There is a web client we can use; I forgot about that until you mentioned IMAP. If it’s got sane text editing and an OK calendar, I might be able to switch to it.
I was taken aback when I first found out the Notes client app is a customized Eclipse build.
I remember Domino Web Access as being kind of okay, but weird, and never a credible challenger to Outlook. It emerged around the time I had less and less exposure to Notes things; there was also a sort of minified, desktop Notes/Domino server ("DOLS") that could replicate web apps locally for offline use and synchronize when back online. Wild stuff!
As for Eclipse, it's more like IBM found a way to wedge Notes (written in C) into an Eclipse wrapper, likely fueled by the early-aughts mania to make everything a portal/portlet.
Some other apps have used Eclipse as a host, DBeaver for example. Although I believe DBeaver is principally written in Java.
I was taken aback when I first found out the Notes client app is a customized Eclipse build.