SMF (abbreviated from Simple Machines Forum) is an advanced forum application that can be downloaded and used free of charge. Written in php and mysql it has all the features you need to create a forum for smaller or larger communities. It is reliable and user-friendly.
SMF has more advanced control panel than most of the other forums. It allows you to set almost anything you can think of - starting from general forum settings like forum news, forum topics and categories, passing through global forum and member settings, and finishing with layout settings. However, it is well categorized and explained, and any forum administrator would be able to work with it.
SMF is proven to be a very secure forum system. You can personally set what access the forum users will have, no matter whether they are registered forum users or not, moderators, or administrators. All administrative settings require username and password and every action can be IP or time locked. You can also set number of login attempts to your forum for a certain IP address.