Catrinity is a free sans-serif OpenType font. The design intends to be clean and easy, with just enough embellishment to make the characters well distinguishable, and the font as a whole distinguishable from other sans-serif fonts.
Catrinity contains a lot of characters for various languages, plus many symbols, including colorful emoji. More characters will be added in future versions. Here are some examples (a complete list is found on the Characters page):
Greek and Coptic
Catrinity uses OpenType features for ligatures and the placement of diacritical marks. These may not work in all programs. Some programs also offer options to turn these on or off.
Also, the possibility of having colored glyphs in fonts is relatively new, so many programs still show the monochrome fallback glyphs for these.