Is there a tool for Windows to batch-convert a folder of
.lit files to a different format, preferably plain-text?
Calibre does most ebook related conversions including this one.
There is also ConvertLit which is an executable that expands one .lit file but can be wrapped in a batch script.
Both work on most OSs
ABC Amber LIT Converter is an freeware utility which converts your LIT (Microsoft Reader) files to any format you wish (PDF, HTML, CHM, RTF, HLP, DOC, and many more) easily and quickly. The software supports a batch conversion, a run from command line, more than 50 languages. Batch conversion ability allows you to convert a unlimited number of LIT files at a time.