Alternatives to Object-Oriented Programming?

First of all please note that many of the programming languages currently in use (especially "higher level languages") are multi-paradigm. That means you are never building programs which are purely OOP (except if you use Smalltalk or Eiffel to build your big projects maybe).

Have a look at PHP for instance:

• Has many elements of OOP (since version 5)
• Was mostly procedural before
• Has elements of declarative programming (e.g. the array functions)
• Implemented many elements of functional programming (since version 5.4)

Basically PHP is gluing a lot of different paradigms together (and is a "glue language" itself).

Also Java implements a lot of concepts which are not from the Object-Oriented paradigm (e.g. from functional programming).

Have a look on the list of programming languages by type in Wikipedia: https://en.wikipedia.org/wiki/List_of_programming_languages_by_type#Imperative_languages (not 100% accurate).

Functional programming (subset of declerative programming)

• Wideley used in practice (it became part of glued languages like PHP, also Java and many others have implemented concepts of functional programming)
• Many ideas originate in LISP which is definitely worth a look
• You can build whole applications e.g. with Haskell therefore it can "replace" OOP

Procedural programming

• C (as a mostly procedural language) is still one of the most widely used languages
• Many modern glue-languages were procedural in the beginning
• Still many programs are mostly procedural (so if you want it can "replace" OOP)

Logical programming

• Most prominent example is Prolog. This is used for specific tasks that benefit from rule-based logical queries
• Can not "replace" OOP in terms of building a large project but may replace it in other terms

Declarative / Domain-specific languages in general

• Using SQL in your projects? Then they are not purely OOP, SQL is essentially declarative.
• Many domain-specific languages (like CSS) are declarative

Imperative programming in general

• Tons of applications are not "object-oriented" but simply written in imperative style (e.g. assembly)
• Look here for a great thread: https://softwareengineering.stackexchange.com/questions/117092/whats-the-difference-between-imperative-procedural-and-structured-programming

This list is not complete it shall just give an idea. Just note that you usually are using a lot of different paradigms when writing a big application and even each language you are using is implementing multiple paradigms.

OOP is usually considered a good choice for structuring large, complex relationships when modelling data. It is not always the paradigm to go with for many other tasks.

Procedural processing was everything before OOP turned up, has produced some large real world applications (in fact, most of them originally) and many operating systems.

It can certainly be used in large scale products with a minimum of pain, and a maximum of performance

Functional programming is another programming paradigm that is popular, mostly in academics. The best example of a functional programming language is Haskell and Standard ML.

The fundamental difference between functional programming and object oriented programming is that you are programming in the sense of data flow instead of control flow. See the presentation Taming Effects with Functional Programming by Simon Peyton-Jones for a good introduction.

A good example of functional programming used in the industry is Erlang. It is mostly used in telecommunication, distributed and fault tolerant systems. See the presentation Erlang - Software for a concurrent World by Joe Armstrong.

There are also newer functional programming languages that combine functional programming with OOP. Two good examples are F# for the .NET platform and Scala for the Java platform; they can often use existing libraries on the platform written in other languages.

The trend of new programming languages now is Multi-paradigm, where multiple paradigms like object oriented programming and functional programming are combined in the same language.