The Right Stuff
The Zotero website https://www.zotero.org/download/ has all you need:
Other Plug-ins
If you want to get fancy, Zotero has lots of other plug-ins. Some allow you to scan books from barcodes with your iPhone or iPad. Others extract citations from bibliographies in Word documents or other programs and import into Zotero. As Zotero is an open source software, there are many plug-ins created by third-parties.
If you want to access your library of citations across devices or create a shared collection with colleagues, you will need an account.
Register https://www.zotero.org/user/register for a Zotero account.