This app allows you to reduce the size of mobi-format ebook files without any loss of ebook content.
It works by removing the source files that were used during the MOBI creation. If the source files exist in the MOBI file, You can reduce your MOBI file size by more than 30~40%. This app only works locally without going through the server. It allows you to extract texts instantly, real-time.

You can select a MOBI file from local computer, Google Drive, Dropbox, and Box.
This app is absolutely free for those who want to reduce a MOBI file size.