DocFetcher - DocFetcher is a portable German/English open source desktop search application.
TagSpaces - TagSpaces is an open source platform for personal data management. With TagSpaces you can manage and organize the files on your laptop, tablet or smart phone.
SearchMyFiles - Alternative to the standard Search For Files And Folders module of Windows. Duplicates search is also supported.
allTags - allTags is a free, tag based file management application.
dtsearch - dtSearch - The Smart Choice for Text Retrieval since 1991.
Elyse - The free version allows up to 30 tags.