I have used MyBB since I started website hosting in 2003. Absolutely love this software and in my opinion, it is the best. I am very surprised they don't charge for a license.
Anyways, when I saw that they were looking for Beta Testers for the new, not-yet-released, version 1.4 of MyBB, I jumped to the chance.
I want to get to know this version as it is vastly different from the other versions.

Features:

• New Admin CP
• Moderator Control Panel
• Postgres + SQLite Support
• Online status indicator in profile + location
• Better font size handler - callback to a function. HUGE sizes are no longer supported.
• New spider detection system - create & edit search engine spiders detected by MyBB directly via the Admin CP. Assign them to their own custom group, set their theme, language or see when they last visited.
• Additional query debug information for plugins - find out which plugin hooks are adding extra unnecessary queries.
• POST request validation for actions which change/save some sort of data - used to help prevent XSS and CSRF attacks.
• Database server fallover/rotation support
• New calendar with ranged, repeating and single day events. Also supports multiple calendars and calendar permissions.
• Rewritten thread and forum marking system - persistent forum marking as well as automatically marking a forum read when all threads in the forum are read.
• Warning system
• Buddy list support when composing a PM
• Alternative support for reading remote files (CURL)
• Redesigned buddy list window
• Ajax rating system
• Redo buddy management - ajax.
• Promotion System
• AJAX Inline Edit - edited by messages
• Plugin System Changes (Plugin authors can now define a list of MyBB versions their plugin is compatible with, Additional routines for installing/uninstalling plugins to be used to completely remove or install a plugin. Activate and deactivate should now be used to "hide" a plugin from view.)
• COPPA Support
• "Last known IP" logged for users - shown in Admin CP under user management
• yes/no values now stored as integers - less disk usage
• Hide posts by ignored user (expandable via JS)
• Plain text version of the post parser - parse a message as text (specifically for email notifications)
• Settings to disable AJAX based functionality
• Unread PM Notice - inline rather than popup
• PM popup listing all the users when there is more then one recipient.
• Admin option to moderate edited posts as well.
• "Quick Language Select" box shown in the footer.
• Rewritten thread subscriptions & favourites functionality (Favourites feature has completely been removed - no one uses it, if they do, favourites moved over to new system, Users have the following methods of subscription: Do not subscribe, subscribe but no email notification, subscribe and receive instant notification)
• Automatic DST checking via javascript - instantly updates your DST setting if it has changed.
• IPv4 addresses now stored as integers, a lot quicker for searching
• Page numbers pretty
• Post Auto Merger setting in ACP (posting)
• Search this thread
• "Cache handlers" to replace existing cache system (brand new cache methods - xcache, memcache, APC etc)
• Mark forum read by clicking on it using AJAX request
• Search engine friendly URLs (forum-fid, thread-tid, etc)
• Link to Post in Quote
• Javascript form validation
• Mail class which supports SMTP and mail() sending. Configuration done by board settings (method, additional mail() parameters, smtp login details)
• Automatic avatar resizing (forced or user selectable)
• Images for "Reply", "Forward", "Delete" PMs
• AJAX quick reply
• "Parse order" for custom MyCode.
• Change reputation points power to textbox
• Brand new member list
• Rewritten "Send Thread to a Friend" and "Send (username) an Email" features (Guest access disabled, message wrapping, logging, inline errors)
• Refresh link for Captcha inputs (JS based)
• Multi-quote on new thread pages
• Search terms (when coming from search.php) should be highlighted in showthread
• Error Handler Class
• Thread authors listed below the subject on forum display
• New/unread threads in forum display bolded
• Select option on theme list in Admin CP "Force users to theme"
• Add editor to signature editor
• Multibyte check during installation - show similarly to supported DB types
• Multiple PM recipients (and BCC support)
• Forum home - "x viewing forum"
• Add "N/A" for old reports where thread/post is missing
• Moving PM takes you back to old folder
• Fix up vote/rate - change all to "Rate"
• Attempt cookie path autodetection during installation
• Show reputation power used in a reputation - Positive (+2)

The software is just amazingly good, especially for something that is free to use and customise.

Although this version is not yet available to the general public, you can check out the latest release by downloading it. Just Click Here to be taken to the MyBB 1.2.13 Download page. Download size: 1.02MB

I would highly recommend this software to anyone who has or wish to have an online community. Excellent software that gets a 10/10 from me.

I will be creating some good themes for this new version very soon. So keep an eye on the Design section of this site for those.