There are two native objects: notes and citations. Notes are rich text and so allow web links. There are not note to note or note to citation links, but there is a "Related" attribute, so that one can link within the system. For example, i link citations for standards to main notes about a general standards process or link from the citation for one book in a series to the citations for the book preceding and following.
Within the citation are fields for last accessed time, archive, and rights details -- which has been useful for reminding myself where ebooks are located.
Citations can have child objects: notes, links to URIs (which may themselves have notes), link to files on your machine, and files. I've not used the file and PDF links, and linked to evernote when i wanted more extensive details. I suppose i could explore attaching files when the richtext notes is insufficient.
- both tagging and collection (cf "notebook") organization, and the objects can be in multiple collections (instead of one notebook per note in evernote)
- browser plugin makes recording citation to on-web items more easy (or very easy, depending on how accurately you want your metadata recorded.
Neutral (for me):
- sharing isn't possible at the item level. One makes a new collection and the can share from there.
- no note to note links but can use the related attribute.
- "If you need images to sync in Zotero, you should add them as separate attachment files."
- no encryption
- What about Mobile? Giving Android app "Zoo for Zotero" by Michael Johnston a try. Of the other two listed one is read only and the other no longer exists.