Appserver.io is an application server for PHP based web environments. The project consists of middleware which delivers classical PHP web applications and provides additional services.
The basic idea of a WildFly equivalent for PHP was present within TechDivision well before July 2013 when development on the project began, due to technical shortcomings of PHP language.
At this time the possibility of a non-blocking, socket -based PHP middleware was given by using an asynchronous event driven workflow or forked processes .   In parallel, as of August 2012, a threading extension for PHP by Joe Watkins enabled true POSIX multithreading compatible.  Controversially  threads were used because they allow the programmer to account for hardware use instead of relying on the used runtime.
After deciding on the technical blueprint, development began on the GitHub platform. As of 2015 , the project consisted of 36 separate repositories , around 80,000 lines of code and estimated effort of 18 years ( COCOMO model). 
Appserver.io is open-source software under OSL in version 3.0. It can be downloaded either as an installable package from the project page, or as a source from GitHub. The project aims at a freemium marketing approach and the splitting of the software into a Community, Professional and an Enterprise Edition.  As of 2015 , the Community Edition  contains all basic features and is open source and free of charge.
As of 2015 , the Professional Edition  could only be used within the Microsoft Azure cloud service and offers additional developer support.
PHP extensions and service daemons, PHP extensions and service libraries, PHP extensions and service daemons.  It is an out-of-the-box runtime environment for PHP development. The use of a multithreading environment is considered to be a so-called shared nothing concept of PHP. 
Together with the bundled runtime, appserver.io bundles administration. As of version 0.6.0 application management is implemented with file-based application deployment.
Appserver.io offers servlets , objects that persist between client requests. These can eliminate repeated bootstrapping of applications, but require the wrapping of bootstrap parts. Appserver.io offers an Enterprise Bean implementation similar to Enterprise Java Beans functionality.
Appserver.io offers modular services that can be used individually by internal and external applications.
- Persistence Container
- Message Queue
- Servlet Engine
- AOP support
- Design by Contract support
- Annotation based Dependency Injection
- Timer service
- Deployment API
- Integrated FastCGI client and backend
- Enterprise Beans similar to Enterprise Java Beans
Appserver.io allows component-based scalability. Services and servers (eg an HTTP webserver) are adjustable in size and number based on an XML configuration file. Additional components can be configured for remote access, allowing for distributed systems and component replication.
As of 2014 , appserver.io was in an early stage of development. The project has been tested, pre-release versions over GitHub. The following list contains versions released up to that date.
Appserver.io beta versions
|0.5.7||10. October 2013|
|0.5.8||5. February 2014|
|0.5.9||13. February 2014|
|0.6.0||9. May 2014|
|0.7.0||14. July 2014|
|0.8.0||22. July 2014|
|0.9.0||23. July 2014|
|0.10.0||23. October 2014|
|0.11.0||27. November 2014|
|1.0.0rc||19. January 2015|
|1.1.0rc||6. November 2015|
Development releases are regularly published over the homepage.
|1.0.0 “Iron Horse”||16. February 2015|
|1.1.0 “Iron Knight”||11. November 2015|
Appserver.io follows a naming convention based on major and minor version numbers. The major digit specifies a context for minor version names exist. The 1. *. * Major version is named Iron which stands for a mythological view on the medieval age . Every minor version 1.x. * within this major release.
- 0.5.8 Windows support with a guided installation procedure
- 0.6.0 web server and modules structure ensured compatibility with non-servlet applications
- 0.10.0 separate application
- 0.10.0 enterprise beans
- 1.0.0 stable API defined by so-called PSRs  (similar to Java Specification Requests )
- Meyen, Sebastian (18 December 2013). Software Development Trends: Wegweisende Beiträge für eine neue IT: Wegweisende Beiträge für eine neue IT . entwickler.Press. pp. 25-49. ISBN 978-3-86802-638-2 .
- Piech, Guido (2014): Online plattform für den Einzelhandel. Das digitale Schaufenster ist erröffnet. In: IT MITTELSTAND, Ausgabe 1-2 (2014), S. 54-64.
- Sitepoint: An Interview with the Appserver.io Crew
- Dev-metal: Postmodern PHP – appserver.io, a multithreaded application server for PHP, written in PHP
- SitePoint PHP Blog: An Interview with the Appserver.io Crew
- SuperbCrew: Interview with Josef Willkommer from Appserver.io Team