Marker.to is described as 'simple annotation tool' and is an website in the Office & Productivity category. There are six alternatives to Marker.to, not only websites but also apps for a variety of platforms, including Google Chrome, iPhone, iPad and Firefox. The best alternative is Diigo, which is free. Other great sites and apps similar to Marker.to are Liner (Freemium), Kjuicer (Freemium), Snippet (Freemium) and Pull - Design Your Post With Style and Share (Free).
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.