Thanks for the links! I knew about Rambox, but wasn't aware of Franz. Looks excellent.
My main problem with Rambox when I first tried it was that it couldn't remember my sessions across restarts for some reason. A quick test shows that Franz doesn't have this problem.
Also, the API for adding new integrations looks delightfully simple [1]! I'll probably take some time over the weekend to try to port over some of the things I use frequently that aren't yet available. Though it'd be even better if it offered a first-class escape hatch to add simple integrations through the app itself like Rambox does.
[1] https://github.com/meetfranz/plugins/blob/master/docs/integr...