This project aims to create a cross-platform tool to easily rename many files at once. So far, the only tools I've found to fulfil this purpose are pure regex tools with no real overview of what is happening. In Mareto, you get the overview, you get the regex (eventually), and you get to edit the names manually without having to close and open a renaming dialog individually for each file.
This project is in early alpha state and is lacking a lot of planned functionality. To see what is currently planned, see the roadmap.
Note: while this aims to be a cross-platform application, it is only being tested on x86_64 linux right now.