XHProf, a PHP extension formerly created and maintained by Facebook, has for many years been the de-facto standard in profiling Drupal's PHP code and performance issues. Unfortunately, as Facebook has matured and shifted resources, the XHProf extension maintenance tailed off around the time of the PHP 7.0 era, and now that we're hitting PHP 7.1, even some sparsely-maintained forks are difficult (if not impossible) to get running with newer versions of PHP.
Tideways has basically taken on the XHProf extension, updated it for modern PHP versions, but also re-branded it to be named 'Tideways' instead of 'XHProf'. This has created a little confusion, since Tideways also offers a branded and proprietary service for aggregating and displaying profiling information through Tideways.io. But you can use Tideways completely independent from Tideways.io, as a drop-in replacement for XHProf. And you can even browse profiling results using the same old XHProf UI!