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.
tcr The .tcr filename extension is a compressed text file format for eBooks and text associated with eBook reader software developed by Psion, a London based techonology company. The format has its beginnings in the early 90's and was designed for use on the PDAs released by the company, particularly the Series 3 handheld PDA. Though the format is proprietary and was intended for exclusive use on Psion devices, today, a few eBook reader applications can open files encoded in this format. As PDAs eventually lost there popularity, the format was discontinued when Psion eventually pulled out of the PDA market.