I regularly contribute to various WordPress plugins and have been contributing to several major plugins throughout the years. The list below includes a few of the plugins that I have contributed to.

Site Kit by Google – Analytics, Search Console, AdSense, Speed
Site Kit is a one-stop solution for WordPress users to use everything Google has to offer to make them successful on the web.

Performance Lab
Performance plugin from the WordPress Performance Team, which is a collection of standalone performance modules.

Yoast SEO
Improve your WordPress SEO: Write better content and have a fully optimized WordPress site using the Yoast SEO plugin.

AMP
An easier path to great Page Experience for everyone. Powered by AMP.

PWA
WordPress feature plugin to bring Progressive Web App (PWA) capabilities to Core

WP Multi Network
Turn your WordPress Multisite installation into many multisite networks, surrounding one global set of users.

Easy Digital Downloads – Sell Digital Files (eCommerce Store & Payments Made Easy)
The #1 eCommerce plugin to sell digital products. Manage eCommerce orders, increase store revenue & accept credit card payments with Stripe + PayPal.

Gutenberg
The Gutenberg plugin provides editing, customization, and site building features to WordPress. This beta plugin allows you to test bleeding-edge featu …

PHP Compatibility Checker
Make sure your plugins and themes are compatible with newer PHP versions.
Occasionally, I also work on plugins of my own. Over the years I have created and published a number of plugins in the WordPress plugin repository, all of which you can download and install on your WordPress site for free. Below you see a list of my plugins; note that some of them are no longer actively maintained. Please refer to the respective plugin readme for more information.

Bootstrap for Contact Form 7
This plugin modifies the output of the popular Contact Form 7 plugin to be styled in compliance with themes using the Bootstrap CSS framework.

Native Lazyload
Lazy-loads media using the native browser feature.

Attachment Taxonomies
This plugin adds categories and tags to the WordPress media library – lightweight and developer-friendly.

WP GDPR Cookie Notice
Simple performant cookie consent notice that supports AMP, Web Stories, granular cookie control and live preview customization.

WP Multi Network
Turn your WordPress Multisite installation into many multisite networks, surrounding one global set of users.

WP-API JSON Feed
Implements a JSON feed following the version 1 spec by means of a REST API endpoint.

Torro Forms Bootstrap Markup
This Torro Forms extension modifies the output of your forms to be styled in compliance with themes using the Boostrap CSS Framework.

Share Target
Allows to share images and other content directly to a WordPress site through the Web Share Target API.
Donations
All the above plugins can be used completely free forever. However, if you like any of these plugins, I would be glad if you donated some money to me. This encourages me to develop more WordPress plugins like the ones above.