Everygamegoing is a huge marketplace of games, aiming to cover everything ever released in United States, Europe and Japan. It has a wealth of formats and over 2 million items (although many items feature the same actual game, because of all the regional differences between releases).
Everygamegoing was built on Yii 1.1, adapted with Bootstrap 4. Originally the site was a PHP 5-powered site but was (slowly) converted to Yii over a period of about a year. Since moving it to Yii the site positively flies along and I have learned a great deal about optimising the queries passed over the past few years.
Yii Version: 1.1