The main back-end web development languages are:

• Python
• Ruby
• PHP
• Java
• JavaScript (Node.js)
• C#
• Go

Each language has its own strengths and weaknesses and the choice of language for a back-end project often depends on the specific requirements of the project and the developer’s skills and experience.

For example:

• Python is a popular language for scientific computing, data analysis, and artificial intelligence.
• Ruby is known for its elegant syntax and is popular for building web applications using the Ruby on Rails framework.
• PHP is a widely-used language for building server-side web applications and content management systems.
• Java is a highly scalable, multi-threaded, and object-oriented language often used for building large enterprise applications.
• JavaScript (Node.js) is a popular choice for building real-time applications due to its event-driven, non-blocking I/O model.
• C# is widely used for building Windows desktop and server applications and is popular in the gaming industry.
• Go is a statically-typed language with strong concurrency support, often used for building scalable and performant systems.

Ultimately, the best language for a back-end project depends on the specific requirements and the team’s skills and preferences.