The Exec-PHP plugin executes PHP code in posts, pages and text widgets.
Even as this plugin hasn't been updated in a while it is an essential addition to WP. I use it for adding PHP code to the widget area of my websites. Careful handling is advised though, as PHP execution in posts, pages and widget areas can lead to unforeseen consequences. But if you know what you're doing, this is the right plugin for the job!
This plugin, although not updated for years, I still found it to be the best solution for writing HTML/PHP code into posts/pages/widgets. I have tried many other solutions, but none stands out as this. The only reasons I haven't rated it 5 stars are:
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