Unlicensed games generally refer to games that are not licensed for development by the original console manufacturer.
This kind of practice started back 1977 when the only developers at the time were working for the original console manufacturer. Atari programmers David Crane, Larry Kaplan, Alan Miller, and Bob Whitehead met with Atari CEO Ray Kassar to demand that the company treat developers as record labels treated musicians, with royalties and their names on game boxes. They would later start up Activision where they began making their own games and cartridges for the Atari 2600 and due to the lack of any kind of lockout for the Atari 2600, it was easy for anyone to make games. Atari had trouble keeping up with all these third-party companies and due to the lack of quality control, the market became over-saturated with 3rd-party titles and it ultimately led to the North American video game crash of 1983. Mattel's Intellivision II and the Colecovision did have ways of locking out games but these were done through the console-only and were really easy to work around.
Around this time, Nintendo's Famicom was released in Japan. It did have a license policy for 3rd-party publishers but there was no lockout method, meaning it was easy to produce unlicensed games for the Famicom. However, the license policy wasn't exactly strict so unlicensed Japanese Famicom games were very rare. Part of the policy did force anyone who signed the contract to develop games only for the Famicom, causing Namco at one point to stop producing games for the system and support Nintendo's rivals. One of the most notable Japanese unlicensed games was Super Maruo, the first unlicensed Famicom game as well as the first pornographic game for that system. However, due to it's high price at the time, this resulted in the game having low sales and not only becoming one of the rarest Famicom games but it also didn't have much of an impact. The lack of any lockout technology on the Famicom or its carts made it easy to clone the console for other countries and let other developers make games for the system. In 1986, Nintendo released the Famicom Disk System which released games on floppy disks. Despite having some well-known titles for the peripheral, the weak copy-protection made piracy rampant for the accessory and it was easy for developers to make unlicensed games for it.
Due to the third-party issue Atari had which ultimately led to the North American video game crash of 1983, when Nintendo brought the Famicom and redesigned and relabeled it into the Nintendo Entertainment System, they implemented a strict third-party licensing policy as well as the 10NES chip in their console and games. The contract forced them to only develop games for the NES, require them to pay for at least 10,000 cartridges that Nintendo themselves would manufacture, only 5 games could be published a year and Nintendo can decide which games can or can't be published. While some of these companies found ways around the contract (Ex: Konami establishing the Ultra Games brand to publish more games than the contract needed), others didn't agree and attempted to find ways around the lockout method. One notable method used by Tengen was the "Rabbit Chip" which essentially acted like the 10NES chip found inside of the game carts. However, Nintendo would later sue Tengen for copyright infringement. Given how not only was the Famicom hardware was easier to obtain but also the use of the chip generally kept bootleg developers away
With the release of the Sega Genesis, third-party publishers began moving over to that system due to its less restrictive licensing system. However, their third-party policy still forces publishers to only develop games for Sega. Because of this as well as the costs behind it, Accolade decided to produce unlicensed games for the system. Sega's lockout method involved part of the console's code known as TMSS (Trademark Security System) that would look for a string called “SEGA” within the game and if it finds it, it'll not only let the game run but display the message: "Produced by or under license from Sega Enterprises, Ltd.". Accolade was able to identify this code, produce the games they wanted and Sega filed a lawsuit against them. Accolade won and was later granted a license by Sega. Other companies such as Wisdom Tree and Realtec have also distributed unlicensed Genesis games in the US to produce games cheaper. In Japan, the only two notable unlicensed Mega Drive games were Dial Q o Mawase! and Divine Sealing, possibly due to the system's performance in Japan. In a similar fashion to the Famicom, the Genesis has also been unofficially released in other territories where Sega has had no control over it.
In response to Sega's third-party policy, Nintendo has also loosened it's own policy for the Super Nintendo Entertainment System albeit using a similar, improved lockout method for their games. This in turned made it much harder to develop games without a license from Nintendo and only very few unlicensed games have been made. The only US unlicensed game released was Super 3D Noah's Ark which instead of being a normal cart that has the ability to fool the SNES into running it, it was a lock-on cart where you would insert a licensed SNES game into the slot and the signals from the chip in the licensed cart was sent down through the lock-on device and into the SNES, triggering the SNES to run Super 3D Noah's Ark. The Super Famicom had a few Japanese unlicensed games near the end of it's lifespan, notably Hong Kong 97 and the adult SM Choukyoushi Hitomi games.
After the fourth generation of games, unlicensed games for consoles in the main video game markets were almost nowhere to be found. This can be contributed to the rise in PCs as a gaming platform as well as mobile devices due to their lack of need of an actual license to be produced. However, in markets where 8-bit and 16-bit consoles were still holding up, various bootleg and unlicensed games were continued to be made for these systems. The only notable commercially sold unlicensed game was MaxPlay Classic Games which was released for the PS2 and GameCube in 2004 which just consisted of 10 Game Boy Advance games running on an emulator. However, some people have developed homebrew games for consoles no longer being marketed, sometimes selling carts of these games online or at conventions.
Unlicensed games and BootlegGames Wiki
For BootlegGames Wiki, we only document unlicensed games from the third console generation (Examples: NES, Sega Master System) and afterwards. While third-party second console generation games could be looked as "unlicensed", the fact there was no third-party policy established by any console manufacturers during that time technically meant there was no license to make any games.
Homebrew games also don't deserve a mention even if they end up ending on a pirate cart from a manufacturer. While they are technically unlicensed, they are generally done as a hobby and aren't sold by publishers.