Software Details
Zotero is a citation management application that can easily replace Endnote. It comes as a plugin for Firefox, or as a separate application that can work in conjunction with other browsers. The Zotero plugin for LibreOffice makes it easy to cite sources and generate bibliographies in many styles - including APA.
Requirements
Available for Mac, Windows, and Linux
Reviews
I have been teaching new pre-service teachers to use Zotero for their college writing for 4 years now. They are amazed at how much time it saves them. I've also been sharing Zotero with faculty in our College of Education for the same period, and they are very satisfied. Several have imported their Endnote libraries, others have just used Zotero from the start. I like that it integrates with Firefox, as I prefer that students use that browser.
Most of our University library databases (ie ERIC by Ebscohost) now list Zotero as one citation export option, making it very straightforward to collect citation details. The Zotero/Firefox integration is highly intelligent, a "Save to Zotero" icon appears in the URL bar for nearly every possible site that you might want to collect citation detail from.
The nicest part is writing in LibreOffice with the Zotero plugin. It's a few clicks to embed the citation, and a single click to generate your bibliography upon completion. So many hours saved.