I'm in the process of beginning a new project and I'm debating on what framework to use. Of course it will be Zope 3, but why do I use it. Well, it's sure something that has to do with these facts:

• it's open source, with a strong, mature community around it
• while it's still actively development, it has a stable API
  

• it's written in Python, one of the easiest and most powerful languages
• it's built around a component architecture, which means writing pluggable applications comes naturally
• solves the problem of publishing objects through the web
• everything is transaction based. You won't lose data with it, you won't get garbage data inside your database
• it has fast, configurable storages (ZODB, Relstorage)
• internationalization and localization is easy
• it's a library as much as it is an application server. When it's a library, it's very slim and as a full application server has a lot going on, including XMLRPC, ftp, webdav, sql connectivity, its own http server, etc.
• has a cool, extensible templating language (the Zope Page Templates)
  
• makes it extremely easy to create and store objects through ZODB
• has facilities to query for objects using indexed data, through zope.catalog and extensions
• writing a new catalog index is not an extremely complex task
• it has an event framework; no complex application should run without an event framework
• has advanced, flexible form libraries that can generate forms introspected from the models (zope.formlib, z3c.form)
• has advanced templating concepts and content placement, such as the pagelets and viewlets
• it's "enterprise ready": it's possible to load balance zope clients using ZEO or relstorage
• comes with extensible authentication and user sources
  
• promotes an extensible build system for applications (zc.buildout)
• follows python standards, for the most part: library packaged as independent eggs and while it's not built around WSGI, it has full support for it
• it can do document workflows (hurry.workflow)
  
• it has some very cool packages from the community:
• zc.table
• z3c.form
• Storm and sqlalchemy wrappers
• zc.resourcelibrary, z3c.resourceinclude
• z3c.pagelet
• lovely.remotetask
• grok
• gocept.registration
• z3c.traverser
  

• is very well documented
• it fits comfortably in my brain