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Pro Open source and free
Pro Easy to filter through fonts
Within categories such as serif, sans serif, monospace, etc, you can adjust desired thickness, slant, width and script to filter the collection of fonts. Additionally, you can also set how you wish to order the fonts (by popularity, alphabet, date added, etc).
Pro Live preview
You can live preview fonts in multiple ways - you can view a single word, a sentence or a paragraph with text and font-size of your choice. There's also a poster view that tries putting more fonts on screen at a time by showing only their name without the option of entering your own text, and is the only view option that allows inverting background and text colors.
Pro Sizable collection of fonts
There are more than 600 fonts to choose from.
Pro In-depth font comparison
Once you've added at least two fonts to your collection you can compare them closely by overlapping them in the compare view. Simply click the review tab at the bottom and navigate to compare tab at the top.
Pro Great for web designers
This repository was designed specifically for web designers. As such it shows the impact of the font choice on page load time, allows selecting only the font styles and sets you need to reduce overhead, and gives multiple methods of integrating the fonts into your website.
Pro Integrates with Typecast
With fonts you wish to use selected, go to review tab at the bottom and click 'Try in Typecast' at the top. Typecast has an easy to use WYSIWYG editor that allows quickly prototyping and testing out chosen fonts.