Electronic books (eBooks) are digital documents designed for distribution across the internet and between mobile devices, and are slowly growing in popularity.
eBooks with the .lit (standing for literature) extension can be opened using an application called 'Microsoft Reader', which is a free application (although activation is required) from Microsoft. Microsoft Reader has been available since 2000, and is now bundled with many of Microsoft's mobile devices.
The .lit file format is based on Microsoft's compressed HTML Help file format. Due to the compressed nature of the file format, eBooks are almost exclusively available from online stores as they're relatively quick to download.