1. Introduction of the game:
"Need for Speed: No Limits" is a thrilling mobile racing game developed by Firemonkeys Studios and published by Electronic Arts (EA). It's a game designed to deliver an adrenaline-pumping experience as players race through urban landscapes at breakneck speeds. Tailored for avid racing enthusiasts, the game merges high-octane action with strategic vehicle customization, ensuring every player can leave their unique stamp on the race track.

2. All characters and levels of the game:
This installment of the "Need for Speed" series doesn't primarily focus on characters as it is a racing game. However, it features a range of non-playable characters (NPCs) that players encounter in various events and storylines. The game boasts an extensive number of levels, divided among different race types such as Sprint Races, Time Trials, and Special Events. Each level pushes the player's driving skills to the limit while they navigate through the game's compelling narrative.

3. What attracts users most to the game:
Users are particularly attracted to "Need for Speed: No Limits" for its stunning graphics, a vast array of drool-worthy licensed cars, and the ability to customize these speed machines right down to the wheels and paint job. The intuitive controls coupled with the exhilarating sensation of speed keep players coming back for more. The game's regular updates, featuring new cars and events, also help maintain its appeal.

4. Why it is popular:
The game's popularity stems from the storied legacy of the "Need for Speed" franchise, known for its immersive racing experiences. Additionally, its free-to-play model with in-app purchases opens it up to a broad audience. The game's social elements, including competing against friends and global players, further enhance its widespread appeal.

5. When the game was released and how many versions are currently available:
"Need for Speed: No Limits" was released on September 30, 2015. Since its launch, the game has undergone various updates and seasonal content additions rather than versions in the conventional sense. These updates ensure that the game remains fresh and engaging for its community.

6. The most difficult part of the game:
One of the most challenging aspects of "Need for Speed: No Limits" for players is the progression system that requires careful management of resources. High-end races and the acquisition of top-tier cars can be particularly demanding. Players often face stiff competition in Special Events, which require a combination of skill, strategy, and sometimes in-game purchases to succeed.

7. Strengths and weaknesses of the game:
Strengths of "Need for Speed: No Limits" include its immersive gameplay, easy-to-learn mechanics, and exceptional visual fidelity on mobile platforms. The game's weakness, however, lies in its freemium model that can lead to a grind-heavy experience or incentivize in-app purchases to progress at a more reasonable pace.

8. What other games have been developed by the same developer:
Firemonkeys Studios, the developer behind "Need for Speed: No Limits," has also developed other popular mobile titles such as the "Real Racing" series, known for its realistic driving simulation and high-fidelity graphics. They have contributed significantly to mobile gaming with their focus on delivering quality and engaging experiences across genres.