For a moment there, Lotus Notes appeared to do everything.
The program was a weird combination of email, databases, and workflow that allowed companies to stand up custom applications and deploy them to relevant groups of workers inside Notes.
Also:
… It provided not just your email, but an internal telephone directory, contact database, booking system for time off, company handbook, and more, all accessible via a single application and a single set of credentials, long before single sign-on became a thing.
Nowadays, it is common for most if not all of these functions to be delivered via separate web-based applications, each requiring a different login so you need to have dozens of different credentials, and each one sporting a different user interface. So I guess you could regard the web browser as an app runtime that is the ultimate successor to Notes?
Also:
Eventually, IBM, which had acquired Lotus in 1995, announced in 2012 that it would be discontinuing the Lotus brand altogether, before offloading Notes to Indian software outfit HCL Technologies in 2018.
The platform still survives, with HCL releasing Domino 14.0 last year, which, as The Register commented at the time, speaks to the “stickiness” of the custom workflows built on the platform.
Also:
But Notes is nowhere near holding the record for the oldest piece of software still being used. The US Defense Contract Management Agency (DCMA), which takes care of contracts for the Department of Defense (DoD), is said to have a program called Mechanization of Contract Administration Services (MOCAS), which was introduced in 1958, making it nearly twice as old.