azw3 The American company Amazon is a recognized powerhouse when it comes to all things related to books. Their proprietary eBook readers dubbed the Kindle which was first released in 2007 is a testament to this. The .azw file format is the filename extension associated with eBooks designed to be read on Amazon's proprietary Kindle device and through their free but closed source Kindle software for smartphones, PCs, and Macs. The format is incompatible with any device other than kindle and its associated software. In order to open files saved in this format on non-kindle devices, one would have to convert the file to another format such as the open ePub format or PDF. Some converters can also convert other formats into .azw files which can later be opened on a kindle device or application.
lit The .lit filename extension, short for literature, is a proprietary filename extension of the eBook file format LIT developed by Microsoft. The format was initially released in 2000 and at the time was only compatible with Microsoft Reader. Though DRM support was one of the strong selling points of the LIT format, wide spread DRM circumvention discounted its utility in favor for competing open formats. This among other reasons caused Microsoft to officially discontinue support for the format by 2011 and cease further sales of eBooks based on the format completely by 2012.