Liberation Mono is styled closer to Liberation Sans than Monotype's Courier New, though its metrics match with Courier New. The Liberation fonts are intended as free, open-source replacements of the aforementioned closed source fonts.
Ranked in these QuestionsQuestion Ranking
Pro Very readable
Liberation Mono works well with hinting on high-resolution displays.
Pro Compact line height
Just like Courier New (the metrics of which this font emulates), its line height isn't too big, which results in more lines on the screen, compared to Consolas and several other more popular fonts.
Pro Has Bold typeface
Con Difference between "0" and "O" isn't clear
It can be difficult to tell the difference between the number "0" and the letter "O". However, the Fedora Project has a slightly altered version of Liberation Mono that fixes this with a dotted zero.