phZorro is a free and opensource forum system powered by core PHP, HTML and core Javascript. It is very small in code base(around 1 MB). It is very easy to install. This system can have unlimited forums.

• Only clean HTML files is used, with no PHP code injected
• Super easy to edit/update/replace any HTML form
• Secured against SQL injection
• You can set admin, moderator or normal user type on any user
• Every admin can also set user type

• You can create multiple forums
• Email verification on signup
• Lost password reset on email
• Users can create news posts
• Users can add emojis in posts
• Users can add images in posts
• Users can add effects and animations on images in posts
• Users can add pricetags on images in posts
• Latest news
• Most read
• Recent posts
• Newest groups

Forum posts is also perfect for advertising, because you can create news posts, or create posts and replies with images and pricetags.
Try it out. It is very easy to install.