1. **Introduction of the game:**
Angry Birds is a captivating and widely celebrated physics-based puzzle game developed by Rovio Entertainment. The game involves using a slingshot to launch birds at structures with the aim of hitting pigs protected within or around these structures. The main objective of each level is to eliminate all the pigs, utilizing as few birds as possible, while also causing maximum destruction to score high points.

2. **All characters and levels of the game:**
The game features a variety of colorful bird characters, each with unique abilities. The most recognizable characters include Red, Chuck, Bomb, Matilda, the Blues, and Terence, among others. On the other side are the green pigs, who vary in size and resilience. Levels are organized into different episodes or themes, with the game originally launching with a few episodes and expanding over time with updates. Levels increase in complexity as players progress, introducing new types of structures and challenges.

3. **What attracts users most to the game:**
Users are attracted to Angry Birds by its simple yet engaging gameplay, charming characters, and the satisfaction of mastering the physics-based challenges. The game's intuitive controls, coupled with the gradual introduction of new mechanics and bird abilities, keep the gameplay fresh and interesting. The social aspect of sharing scores and competing with friends also adds to the game's appeal.

4. **Why it is popular:**
Angry Birds gained popularity due to its accessibility, entertaining animations, and addictive quality. It translates the familiar concept of knocking down structures with a unique and humorous twist. It also became a cultural phenomenon through clever marketing, a multitude of merchandise, and even adaptations in film and television, which helped solidify its popularity.

5. **When the game was released and how many versions are currently available:**
The original Angry Birds game was released in December 2009. Since then, Rovio Entertainment has released numerous versions and spin-offs, including Angry Birds Seasons, Angry Birds Rio, and Angry Birds Space, to name a few. The franchise has expanded to include over 10 different games, with multiple editions and special updates to keep the series fresh and engaging.

6. **The most difficult part of the game:**
The difficulty in Angry Birds often arises in the later levels, where complex structures and tougher pigs require precise shots and strategic use of birds' skills. Mastering the trajectory and timing to achieve three-star ratings on all levels can be exceptionally challenging, providing players with a rigorous test of their puzzle-solving abilities.

7. **Strengths and weaknesses of the game:**
Strengths of Angry Birds include its straightforward gameplay, appealing graphics, and wide range of levels that offer countless hours of entertainment. The game's humor and character design also add to its charm. However, weaknesses might include occasional repetitiveness, and for some players, the reliance on in-app purchases to advance through levels quicker or to access additional content may be a downside.

8. **What other games have been developed by the same developer:**
Rovio Entertainment, the developer behind Angry Birds, has produced several other games and spin-offs. Some notable titles include the various Angry Birds sequels and themed games, "Bad Piggies" which allows players to play as the pigs, and "Angry Birds Transformers." They have also ventured outside the Angry Birds franchise with games like "Battle Bay" and "Small Town Murders."