Magento Open Source platform, formerly known as Magento Community Edition, has outstanding codebase which allow you to extend almost any part of your store. You can find a lot of really useful free and premium magento extensions which makes store owner life much easier.
Github is a great source of free magento 2 extensions. You can check the code, last commit date, author responsivness and get help on your issues from other community members. Check my magento 2 extensions github list below. These are extensions which I do personally use or they are interesting to me and I am following the development.
Administration
Admin Activity by KiwiCommerce
https://github.com/kiwicommerce/magento2-admin-activity
Regeneration URL rewrites of products/categories
https://github.com/olegkoval/magento2-regenerate_url_rewrites
Import/Export
M2IF – Magento 2 Import Framework
https://github.com/techdivision/import
Mobile Applications
Open source React Native mobile app for Magento 2
https://github.com/troublediehard/magento-react-native
Social Networks
Magento 2 Social Login
https://github.com/mageplaza/magento-2-social-login
GDPR Policy
Magento 2 Enhanced Privacy
https://github.com/flurrybox/enhanced-privacy
Image Optimization
Magento 2 Image Optimizer
https://github.com/justbetter/magento2-image-optimizer
Search Engine
Smile ElasticSuite – Magento 2 merchandising and search engine
https://github.com/Smile-SA/elasticsuite
PWA Alternative
Vue Storefront – PWA for eCommerce
https://github.com/DivanteLtd/vue-storefront
WordPress Integration
WordPress integration for Magento 2
https://github.com/bentideswell/magento2-wordpress-integration
Magento 2 Blogs
Magento 2 Blog by Mageplaza
https://github.com/mageplaza/magento-2-blog
Magento 2 Blog by Magefan
https://github.com/magefan/module-blog
Magento 2 Blog by Mirasvit
https://github.com/mirasvit/module-blog
SMTP Modules
Magento 2 SMTP by Mageplaza
https://github.com/mageplaza/magento-2-smtp
Magento 2 SMTP by MagePal
https://github.com/magepal/magento2-gmail-smtp-app
Developer
Developer Toolbar for Magento2
https://github.com/vpietri/magento2-developer-quickdevbar
Wrap Up
Feel free to post more github repositories links in comments. We will update the list with the most interesting extensions. More magento 2 extensions can be found using this link – https://github.com/topics/magento2-extension
You might also find interesting 10 Codecanyon Top Selling Magento Extensions in 2018