I recently made an online fb2 to lrf converter for Sony Reader. The reason was the lack of a utility for poppy and the presence of a free console converter by Mikhail Sharonov.
To work, you must select the fb2-file or zip-archive with one fb2-file and click on the "Convert" button. ')
Suggestions and criticism are welcome.
UPD. Now you can convert multiple files at the same time by specifying links to files on the Internet. True, it takes decent time. :) I will try to find the reason.
UPD2. Pick up the result can now be in the form of a single zip-archive.
UPD3. You can choose one of three fonts: standard, Garamond and Verdana.