When comparing Nextcloud Mail vs Zimbra Web Client, the Slant community recommends Nextcloud Mail for most people. In the question“What are the best self-hosted webmail clients?” Nextcloud Mail is ranked 11th while Zimbra Web Client is ranked 12th.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Open-source, self-hosted, connects to major servers (Gmail, Outlook, etc)
Pro Maintained by the Nextcloud organization
Pro Full-featured collaboration solution
If you are looking for an alternative to Gmail, look no further than Zimbra. While not a complete document solution it does have some document features as well.
Cons
Con Not perfectly stable yet
Still in development, no 1.x release. Random hickups / crashes that require reloading the page.
Con Heavy and monolithic
Zimbra doesn't much work with its host platform as much as it brings its own copies of utilities. If you want something small and "plays well with others" integratable...this is not it. Too heavy to run on a RaspberryPi if you're looking for something for just a few users.
Con Linux only
There is no installator for Windows