SMDB is a small, portable database library that exports an API similar that of GDBM and allows for the simple storage and retrieval of key/data couples. The library is totally system independent due to the use of externally supplied interface pointers. File locking is left to the caller, allowing single instance users to not pay the the price (in terms of performance and portability) of the locking framework. It supports transactions, multiple tables inside the same DB file, and is less than half the size of GDBM.
eXtcos is an extensible JVM component scanner, similar to the component scanning feature of Spring. It is a small library solely focused on the task of class path scanning. It provides an easy-to-use query language for requesting the classes. This is a refreshing change to the boiler plate code you need to use the Spring classes for your own needs. You can get several different kinds of classes with just one query. You can use eXtcos for finding plug-ins for your application, classes meant to be run inside your container or framework, and the like. eXtcos is basically a base library on which other applications, containers, and frameworks can depend on.
OnPosix is a tiny library to abstract POSIX mechanisms to C++ developers. Most features offered by this library can be found either inside the Boost library or in a library compliant with the C++11 standard. Unfortunately, however, for some embedded Linux devices, these libraries cannot represent viable solutions, due to the lack of memory space (for the Boost libraries) and the lack of a new C++ compiler (e.g., on Xilinx MicroBlaze). On these platforms, the OnPosix library represents a good and cheap solution to have object-oriented POSIX mechanisms. The library offers support for threads, mutual exclusion, sockets, logging, timing, etc.
AS3WavSound allows you to embed wav files into your project compiled with the open source Flash SDK compiler. Normally this is not possible and circumvented either by: using a licensed expensive editor that does this for you, or by the very ugly .swf workaround. This library does it natively and cleanly.
Variance provides a general-purpose, custom-wirable junction box for conversion between Java types. Values stored as Variants can be converted freely to any type (provided that a type converter exists between the original type and the target type), and users can add new type converters or override existing conversions.