Here are some amongst the many hundreds of Wordpress plugins I have worked with.

• WP3 Broadcast for sharing content across a number of 'replica' sites in a multi-site network
• Polylang for multiple language support
• Wishlist member (extended) for a paywall
• Wordpress REST v2 API which I extended to provide the functions of a 'headless CMS'
• Advanced Custom Fields

• Customised child themes with branding functions which swapped featured images on each post to fit the branding of the site that the post was being broadcast to
• I worked with a plugin for user data capturing, which allowed WP administrators to create custom registration forms for each promotion or competition, to collect the user data that they needed
• I worked with a plugin for user authentication which used OAuth to validate the user on another server
• A plugin for Google Web analytics tagging which complied with a complex corporate reporting structure of about 20 fields, taking some tags from editorial input and building others in a standard way
• A Most Read plugin which used a very lightweight script on the page to count the page access, even when the page was cached. The counting server was separate from the WP server to separate out the server load. There was also a sampling option for very high volume systems.
• A WP Administrator's plugin designed to help administrators who were new to Wordpress to find where to change the different parts of the site. It could embed links on the front of the site to where in the back end these parts could be edited.

• I looked after a multi-site network on WP Engine.
• I worked with WP hosted on Amazon Web Services, with multiple web servers running identical Wordpress systems, fronted by a load balancer, with a Amazon S3 as a CDN for media files, and a large Amazon RDS, with replication, for the data. I did not set this up, however.
• I worked on a number of Wordpress systems which were hosted by my employer.