[norswap]

The thing I lack in GMail (or other mail clients / services for that matter): the ability to rename conversations, as well as split/fork them according to my wishes.

Anyone know of an alternative that does this?

[xpressyoo]

You can do that with Gmelius (premium tier) by enabling the so-called feature "Edit the subject line in reply and forward".

[mkuhn]

Check out Streak: https://www.streak.com/