PHP engine for the site

It is required to create a site on which topics will be published by the administrator or moderators with limited rights. Topics must be with reader comments. Something like a blog, only readers will register on the site itself.

Which free engine, in your opinion, is optimal for such purposes, given the further possibility of increasing the number of visitors?

The site is planned to be placed on megabytes provided by the hoster, without buying a virtual server.
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Please help, a person who does not understand anything in this matter. ))