Zotero 6
The only thing holding me back from using Zotero is that, afaik, you need to use a Zotero account to reliably sync metadata between devices (the Zotero Data Server isn't supported). I wish it was easier to self-host; there's no reason for me to interact with their servers.<p>It's always a disappointment to find otherwise great open source projects that have key components that deny privacy.