I got my start doing Lotus/Domino development and it was a surprisingly powerful system. We developed all kinds of internal workflow and document management tools that ran basically the entire company. The document store 'database' model it used reminds me very of the NoSQL movement that came over a decade later. One pretty amazing thing at the time (mid-late 90s) was that you also got usable web interface to all your tools almost 'for free' (which is what half the people used). When combined with Lotus 123 it would spit out very nice reports and graphs with only a few lines of code. In many ways it was way ahead of its time and it took years for most other tools to catch up.

One thing we never used Lotus for though was mail, calendar or contacts.