It's a simple Expression Language (EL) for Java, the code base sometime ago was migrated to the Apache commons ognl and this source code is used just to maintenance 3.x branch. The new version from Apache will start from 4.x

Out of incubator and now officially found here http://commons.apache.org/ognl/

• How to run OGNL in Google AppEngine?
  • you need to tell OGNL to not do security manager permission checks, which will fail since GAE has a security manager and you don't have the ability to add the OGNL-specific permissions. Therefore, somewhere in your initialization code, add this OgnlRuntime.setSecurityManager(null);

• makes OgnlContext a bit more immutable
• sets source and target in pom.xml to Java 1.7

• drops access to #context and _classResolver via a magic keys - thanks to Łukasz Lenart

• fixes issue with returning the hasCode method when looking for a field code #32 - thanks to Łukasz Lenart

• fixes issue with returning default methods from interfaces implemented by parent class #30 - thanks to Vlastimil Dolejš

• Does not treat negative numbers as an arithmetic operation #28 - thanks to Łukasz Lenart

• Drops access to _memeberAccess field via a magic key - thanks to Łukasz Lenart

• Exposes flags to allow check if an expression is a chain or an arithmetic operation or a simple method - thanks to Łukasz Lenart

• fixes automatic type conversion to avoid double boxing #25/#26 - thanks to Christian Niessner from secadm GmbH

• fixes issue with selecting overloaded methods #23/#24 - thanks to Christian Niessner from secadm GmbH

• fixes issue with executing expressions on Java 8 plus adds an java like method matching #19 - thanks to marvkis

• Exposes flag to allow check if an expression is a sequence of simple expressions - thanks to Łukasz Lenart

• Fixes accessing statics within Enums OGNL-158 - thanks to Aleksandr Mashchenko

• OgnlRuntime.invokeMethod can throw IllegalAccessException because of hash collisions was fixed OGNL-252 - thanks to Carlos Saona

• support for boolean expression in Strings was added, this can break backward compatibility #8 - thanks to Daniel Fernández

• lots of optimizations which should improve overall performance #9, #10, #11, #12 - thanks to Daniel Fernández
• OGNL supports default methods in interfaces (Java 8) OGNL-249

• fixes problem with cacheKey too expensive to create WW-4485 - thanks to Jasper Rosenberg

• regression bug in ognl for "is..." property getters WW-4462 - if expression doesn't end with () is considered as a name of property a not the method itself thanks to Jasper Rosenberg

• replaced IntHashMap with ConcurrentMap to avoid deadlocks WW-4451 - thanks to Jasper Rosenberg

• added better capitalization logic for methods WW-3909 - thanks to Iwen.ma

• uses better method to calculate method's cache key WW-4113 - thanks to Kevin Su

• important performance improvement OGNL-224 - thanks to Pelladi Gabor
• race condition fix OGNL-226 - thanks to Johno Crawford

• partially reverts previous changes to allow OGNL to work in environment with Security Manager enabled WW-3746

• Adds possibility to discover eval chain

• small fix to improve performance WW-3580

• small fix to solve a problem with compiling under JDK5

• Javassist added back as a dependency WW-3544