GTmetrix is a rather advanced tool that offers a lot on its free tier, but it also offers premium tiers. If you sign up, you can compare multiple websites, multiple versions of the same website, tested under different conditions, and save tests for later viewing.
YSlow is still relevant, although its best days were those when Firebug ruled supreme among the browser inspectors. It offers a Chrome app and other implementations --- such as add-ons for Safari and Opera, a bookmarklet, an extension for PhantomJS, and so on.
For advanced users, PhantomJS integration means that one could, for example, automate the testing of many websites --- hundreds or thousands --- and export the results into the database.
YSlow's Ruleset Matrix has for a number of years been a measuring stick for website performance.
Pingdom Tools is a SaaS service that offers monitoring and reporting of website performance, and it has strengthened its market position in recent years. It also offers a DNS health check and website speed testing on its free tier, which is comparable to GTMetrix and YSlow.
For the purposes of this article, we purchased a fitting domain name --- ttfb.review --- and installed Drupal with some demo content on it. We also installed WordPress on wp.ttfb.review, and demo installations of Yii and Symfony on their respective subdomains.
We used the default WordPress starting installation. For Drupal, we used the Devel and Realistic Dummy Content extensions to generate demo content. For Symfony we used the Symfony demo application, and for Yii we used basic application template.
This way, we'll be able to compare these installations side-by-side, and point out the things that deserve attention.
Please be aware that these are development-level installations, used only for demonstration purposes. They aren't optimized for running in production, so our results are likely to be subpar.