ngsymfonytools-bundle integrates the legacy netgen/ngsymfonytools as a Legacy bundle, a feature introduced in eZ Publish 5.3 (see ezsystems/ezpublish-kernel#719).
Installing this bundle will automatically install (via composer) the legacy extension, and enable it transparently.
It shouldn't be required to install it, since it is required by ezsystems/comments-bundle, and installed by default.
If need be, run composer require ezsystems/ngsymfonytools-bundle:* to your eZ Publish 5 app's composer.json,
and run composer install.
This bundle is under GPL v2.0 license.