COlivri looks for free text in the title and authors and provides filters to refine the search:

• dist:R R kilometers around your location (ex: dist:5)
• tag:tag-name (ex: tag:art)
• group:group-name (ex: group:pylule)
• lang:iso 639-2 trigram (ex: lang:eng, lang:fra, lang:spa)
• user:username (ex: user:eugene)

filters must be explicitly removed (click on x).