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.
Anytxt Desktop Search - Anytxt is Desktop Search Tool with A Powerful Full-Text Search Engine.
allTags - allTags is a free, tag based file management application.
TextSeek - TextSeek helps you search document contents for Windows and MacOS within seconds, including PDF, Word, Excel, PowerPoint, and other formats.
Elyse - The free version allows up to 30 tags.
Everything by Voidtools - Everything. Locate files and folders by name instantly. Everything. Small installation file. Clean and simple user interface.