Liner is described as 'is the only web highlighter that syncs across desktop and mobile. Leave highlights on your favorite news articles, blog posts, text books, PDFs and more!'. There are more than 10 alternatives to Liner for a variety of platforms, including Online / Web-based, Google Chrome, iPad, iPhone and Firefox. The best alternative is Diigo, which is free. Other great apps like Liner are Instapaper (Freemium), Weava (Freemium), scrible (Freemium) and Kjuicer (Freemium).
Instapaper is a simple tool to save web pages for reading later. To save web pages for later offline reading: go to Instapaper.com, install the Read Later bookmark, and mark any pages you'd like to read later.
scrible lets you highlight and annotate web pages and easily save, share and collaborate on your web research with others. Smarter Web reading & research. Annotate, bookmark, save, manage & share online articles.
Pull lets you highlight great quotes and share them as sleek images. Simply select text from the web in Safari and use the Pull Action Extension to get started. You can also access a history of previous Pulls so you can share them again and again.