ReiserFS is a file system designed for Linux operating systems, created by Hans Reiser and his company, Namesys. It was first released in 2001 and is known for its efficient storage management and fast performance, particularly with small files. One of its key features is the use of a balanced tree structure, which allows for quick access and modification of files. ReiserFS also supports advanced features like journaling, which helps protect data integrity by keeping a log of changes before they are committed to the disk.