Packages for Yii3
Yii3 packages are distributed through Composer rather than through the legacy extension catalog.
Yii3-specific packages
Look for packages carrying the yii3 tag on Packagist. These packages are designed specifically for Yii3 applications or provide Yii3 integrations.
Regular PHP packages
You are not limited to packages made specifically for Yii3. Regular framework-independent PHP packages can be installed and used in a Yii3 application through Composer, provided their PHP and dependency requirements are compatible with your project.