Portal Beta refers to Portal during its very interesting development stages from mid 2005 to October 2007. After all the puzzles were finished, the design went through a lot of changes from a Half-Life 2 Nova Prospekt design to the now known Aperture Science clean look. Betas were playable and most of the chambers didn't have bugs.
Name depends on the era of the development. For example: Portal 2005 beta, Portal 2006 Beta etc., however the most common use for Portal Beta is Portal-Project Beta which is a mod that was developed by ReepBlue which contains all maps from each era.
Puzzles were first finished during Portal Development, so the beta was similar to the Retail. There are many versions of test chambers with same puzzles however the plot was different.
Player would wake up in the relaxation vault and would wait 2 minutes until the ticking analog clock finishes. Player would solve all test chambers as in retail and then escaped to the Nova Prospekt facility (lab_lvl maps). During lab_lvl maps, player would approach test chamber 16 with turrets (During that time of the development, Test Chamber 16 wasn't even a test chamber but it was rather an escape map). After the turret chamber player would approach the hallway (lab_lvl3a) and was supposed to find 3 axillary units and put them in the axillary unit chamber to unlock the door which later leads to test chamber 18 (Which was an escape map by title lab_lvl4 and had the same layout as retail). The ending of 2005 is unknown or wasn't even finished.The best mod that recreates this era is Portal: Prospekt.
Early 2006 (Leipzig)
After the developers rejected the Nova Prospekt design, things were slowly changing to the clearer look. Leipzig era kept the combine elevator and the analog clock was still there. The doors took a shape of Star-Trek looking doors. Chamber 13 is the only map that is available from this build.
Portal in 2006 looked very similar to the final product. GLaDOS' voice was different and in some chambers more distorted. Another difference between 2006 and the 2007 Final retail is the escape: The beginning of the escape is the exact same as in the Retail with few changes within the details. The player would later encounter GLaDOS which took an appearance of a rollermine cube and she would talk about the Black Forest cake recipe (that dialogue was later recycled for the blue personality core in the 2007 Retail Escape). The player would redirect the rockets from the rocket turret (like in the retail) to GLaDOS and she would escape to another room where obstacles are more serious. In the second room which is smaller, turrets would still appear and the rocket turret was on the ceiling. When GLaDOS is defeated, the room gets flooded and the room transforms into a dirtier and less finished room and the water would go away. The player could get out. The reason that ending was cut was because play-testers felt guilty chasing something that would later be helpless and killed.
Very close to the final product with lighting changes and the final core where the player confronted GLaDOS was looking less finished (notice the incinerator).
The Leak Drama
Portal Beta files have been tossed by the community a lot. On June 21st someone leaked a previously unreleased restoration mod of the original Portal beta on the Facepunch forums; http://archive.is/PHBSE The leaked beta contained the whole 2006 Portal Campaign (All test chambers and escape battle) and one map from 2005 which was lab_lvl3a.
'Project Beta Group', members of Facepunch's Half-Life/Source modding community, had been given beta and development assets from both Valve and ex-employees in good faith to create a restoration mod showcasing the origins and evolution of the earliest stages of Portal. The assets were loose, partial, or otherwise unfinished, requiring considerable time and effort by the mod team to reconstruct and compile a working, though still raw, build of the mod. That the leak was not simply sharing files already shared by Valve, some of which were never intended to go public, but also negated the unfinished work of a dedicated mod team who had spent years on the project had a predictable outcome on the forums; http://archive.is/Ek1lJ
Here is where the allegations begin.
Valve News Network, a Patreon-funded Valve news/gossip YouTube channel was given an early build of the mod for use in a 2 hour documentary-style video titled 'The Evolution of Portal'. It's alleged that VNN then traded the files without the mod team's permission for similar development assets from early versions of Left 4 Dead to use in a future video.
On June 22nd an established member of the Facepunch community claims to have received a statement from Valve, essentially an email reprimand that said:
Sharing beta content in an uncontrolled fashion, such as with the recent portal content fiasco, is wholly detrimental to the community at large. When such content is shared privately or with mod developers it is usually done in a way that the content can be shared after it has been adjusted for the retail version of the game.
Sharing the development files is usually not allowed without expressed written permission, however it is fine to share mod builds that use imported versions of these art assets. When these community conflicts happen from archives shared in good faith it looks bad for both parties and could be detrimental to the future cooperation between us and the community.
causing many to believe serious harm has been done to the modding communities' relationship with Valve, a company not exactly known for its openness; http://archive.is/ke8Zr#selection-5891.0-5891.8 . Later the modding community managed to reconstruct the broken leaked 2006 maps and made a few 2005 maps based on the lab_lvl3a which contained: Relaxation Vault, Chamber 13, Chamber 18 (lab_lvl4, partially). Other maps (Test Chamber 4 and Test Chamber 8) were based on the vgui .vtf pictures found in the game files of the leaked beta. Project-Beta used those maps to create 2005 campaign which was missing a lot of chambers based on the leaked pictures of the official test chamber design.
The general consensus on Facepunch is that VNN harmed the community to further his channel.
That the leaked files did originate from VNN doesn't appear to be in contention. In his only response so far VNN claims that his motives were only to archive files and information that would have otherwise remained unavailable in the collections of "beta enthusiasts," and that the leak was done by someone with access to his archive upset with this fact; http://archive.is/EEtfC#selection-2021.0-2021.9