What is Symfony? A PHP full-stack web framework. Symfony is written with speed and flexibility in mind. It allows developers to build better and easy to maintain websites with PHP. Symfony can be used to develop all kind of websites, from your personal blog to high traffic ones like Dailymotion or Yahoo! Answers.
What is Yii? A high-performance PHP framework best for developing Web 2.0 applications. Yii comes with: MVC, DAO/ActiveRecord, I18N/L10N, caching, authentication and role-based access control, scaffolding, testing, etc. It can reduce your development time significantly.Symfony and Yii belong to
"Frameworks (Full Stack)" category of the tech stack.
"Open source" is the primary reason why developers consider Symfony over the competitors, whereas
"Open source" was stated as the key factor in picking
Yii.Symfony and Yii are both open source tools. It seems that Symfony with
21.1K GitHub stars and
7.01K forks on GitHub has more adoption than Yii with
4.86K GitHub stars and
2.22K GitHub forks.According to the StackShare community, Symfony has a broader approval, being mentioned in
374 company stacks &
277 developers stacks; compared to Yii, which is listed in
58 company stacks and
32 developer stacks.
UPDATED
article
Dec 10, 2023
80.6% United States of America (the) 
11.1% Russian Federation (the) 
4.9% China