Chegg
The company Chegg provides two similar citation services, BibMe and EasyBib. These are not as robust as other citation managers, but both will provide citation creation for free; with a free account, you can also save citations. Both have paid versions that leverage Chegg's tutoring services.
Clarivate owns the citation manager EndNote, which claims to be "the best reference management tool." There is a free trial available.
PaperPile touts itself to be "the no fuss reference manager for the web." There is a free trial available.
JabRef is a free reference manager. JabRef claims to be functional "on all your devices."
A project of the Corporation for Digital Scholarship, Zotero is a free "personal research assistant." This means that the tool will function as a reference manager but will also provide assistance with research discovery.