Source Han Sans (思源黑體) and Source Han Serif (思源宋體)

Source Han Sans (思源黑體) and Source Han Serif (思源宋體) are open-source font families developed by Adobe in collaboration with Google. These fonts have become highly popular in graphic design and typesetting for several reasons:

1. High Readability and Versatility
Source Han Sans is a sans-serif typeface with clean strokes and a modern aesthetic, making it ideal for digital platforms and print media. On the other hand, Source Han Serif is a serif typeface characterized by thin horizontal and thick vertical strokes, echoing East Asian calligraphy, which is perfect for traditional and classic design projects. Both font families offer seven different weights, ranging from extra light to heavy, allowing for flexible use in various design contexts​ (撰風旅食)​ (维基百科，自由的百科全书).

2. Open Source and Free to Use
Both font families are licensed under the SIL Open Font License (OFL), allowing users to freely download, use, modify, and redistribute the fonts, whether for personal or commercial purposes. This open-source nature eliminates legal concerns, enabling designers to confidently incorporate these fonts into commercial projects​ (撰風旅食).

3. Wide Character Support and Consistency
The Source Han font families are specifically optimized for Chinese, Japanese, and Korean (CJK) languages, ensuring consistent display across different linguistic environments. This broad character coverage has led to the development of numerous derivative fonts, such as Genyo Gothic, Taipei Sans, and Iroha Maru, which further expand the range of stylistic options available to designers​ (懶惰的權利)​ (每日一錠數位內容).

4. Derivative Fonts and Applications
A significant number of derivative fonts have been developed based on the Source Han fonts, including Genwa Gothic, Genseki Gothic, and Genkai Mincho. These derivatives maintain the original features of Source Han fonts while making subtle adjustments to meet specific design needs. For example, Genyo Gothic is a rounded version of Source Han Sans, tailored for a softer and more friendly design aesthetic​ (维基百科，自由的百科全书)​ (blog.justfont).

In conclusion, Source Han Sans and Source Han Serif are favored in design and typesetting due to their high quality, versatility, open-source nature, and extensive character support. These fonts, along with their many derivatives, offer designers a broad range of tools to create visually appealing and consistent designs across multiple languages and styles.