Thanks for your feedback. For a user group like yours (I'm assuming 2-5 users) a hosted option would be best. We are working with several partners now to spin up hosted options for those in the Zimbra community that would like to use Zimbra's Network edition but don't have a large enough user base so afford our small biz edition. See the
pricing for more details on the current license and support options.
If you'd like to discuss this further please contact our sales team:
sales AT zimbra.com
In general though if your price point is zero(aka free as in beer) it going to be hard to get everything you're asking for. The open source edition offers unmatched functionality with ease of use and admin. There no other project that I know that offers the same features with such a rich and updated web client. IMHO your already getting a pretty good deal, but who am I to judge.
A full list of current our features(open source and network) can be found
here. If you know of any other project that offers a superset of this functionality and is also free and open source please post a link. I'd be curious to check them out.