ELM is a multi-purpose library used by the OTAWA project (http://www.otawa.fr). It provides :

generic data structures,
generic interface with te operating system (files, command line, etc),
a checked plugin system,
efficient string class,
other utility classes.

The facilities of ELM (classes, functions, templates, etc) are sorted in the following modules:

Allocation Module – specialized allocators and interactive garbage collector,
Checksum Engines – checksum algorithms,
Data Structures – common generic data structures and associated facilities,
Dynamic Data – data structure implementation using inheritance and virtual methods,
Input / Output System – unformatted and formatted input/output classes,
JSON Module – JSon format ELM implementation,
Network Module – network access abstraction classes,
Command Line Options – command line option parsing classes,
Serialization / unserialization – serialization facilities,
Character String – character string facilities,
System Interface – system abstraction facilities (file system, plugin, random number, process management),
Run-Time Type Information – RTTI type support,
Type Support – type information and other related functions,
util – miscellaneous utility classes (including debugging and testing helper classes),
XOM Module – XML input/output classes.

ELM contains a lot of useful features to make easier the developer life: instead of reading the whole documentation, take a look to Recipes for a short list of more useful features.