https://github.com/demogorgorn/yii2-ajax-submit-button
This is the powerful AjaxSubmitButton widget that renders an ajax button which is very similar to ajaxSubmitButton from Yii1 for Yii 2, but has many useful functions.
https://github.com/johnitvn/yii2-ajaxcrud
Gii CRUD template for Single Page Ajax Administration for yii2
https://github.com/bizley/yii2-migration
Generates migration file based on the existing database table and previous migrations.
https://github.com/bizley/yii2-podium
This extension allows you to add forum to your app. Demo: http://bizley.pl/podium/home
https://github.com/mervick/yii2-material-design-icons
Yii2 Material Design Icons Asset Bundle
https://github.com/webzop/yii2-notifications
Yii2 module to provide a notification managing system
https://github.com/pantera-digital/yii2-rules
Rules module for Yii Framework 2.x gives ability to create and manage reactions for events
https://github.com/digitv/yii2bootstrap4
Bootstrap v4 widgets for Yii2
https://github.com/ruskid/yii2-csv-importer
Yii2 CSV Importer to Database