Is DB2 dead ?
One of my favorite features is the "time travel" query. If you enable this feature on one or more tables you can essentially say "give the results of this query as it would have been at time x". I don't know if anyone else provides that, but it's pretty great stuff.
I'm looking forward to seeing it in PostgreSQL.
[1]: https://www.pgcon.org/events/pgcon_2020/schedule/session/100...