ExternalSort is a class that can sort large files similar to the Unix sort command. It can read the file to be sorted in small buckets associated with temporary files to not exceed the configured PHP memory limits. The buckets are sorted individually and then merged to produce the final sorted output. The class provides command line interface options so it can be executed as a command from a shell.
Plgen (Playlist Generator) is a tool that sorts files for MP3 players in a user defined order. Cheap MP3 players often come with no playlist capabilities. In addition these players often make use of the FAT16/32 file system, leading to confusion when the playing order is not alphabetical on the device even though it is shown as alphabetical in the file explorer.
Opensort is general purpose sorting software that aims to be a fast and easy solution for the sorting of large or small data-sets and data manipulation in general. It is still in the early stages of development and lacks many of the advanced features its commercial counterparts have. For the moment, it only provides a simple command line interface and a C library other programs can use to cover some basic needs for data sorting.
io-util is a small, scalable Java library for slicing and dicing fixed width tables on disk. The objective is to provide reusable blocks of code for building efficient, custom binary data stores. It allows you to build, search, and maintain a large, externally stored, fixed width, sorted table. The library user specifies the row width (in bytes), a row comparison function (which implicitly defines any given row's key), and an optional delete codec.