Lotus Notes was a product far ahead of its time (nearly forgotten today) which was an object database with synchronization semantics. They made a lot of decisions that seem really strange today, like building an email system around it, but that empowered it for long-running business workflows. It's something everybody in the low-code/no-code space really needs to think about.
No one that has ever had to work with Lotus Notes could forget it. It was atrocious. Maybe the sync engine was great but I really do not know what it was used for ...
