Firefox PDF Viewer (PDF.js)
Open Source
PDF.js. A general-purpose, web standards-based platform for parsing and rendering PDFs.
Kami
Commercial
Kami is an online PDF viewer.
Chrome PDF Viewer Plug-in is a built-in PDF viewer in chrome.
Compare Okular with alternatives
Compare Firefox PDF Viewer (PDF.js) and Okular and decide which is most suitable for you.
Compare Chrome PDF Viewer Plug-in and Okular and decide which is most suitable for you.