<Tr> <Th> Locate32 </Th> <Td> Windows </Td> <Td> Graphical port of Unix's locate & updatedb </Td> <Td> BSD License </Td> </Tr> <Tr> <Th> Lookeen </Th> <Td> Windows </Td> <Td> Major Microsoft Windows search product . </Td> <Td> Proprietary (14 - day trial) </Td> </Tr> <Tr> <Th> Nepomuk </Th> <Td> Linux </Td> <Td> Open Source semantic desktop search tool for Linux . Has been replaced by Baloo in KDE Applications from release 4.13 onward . </Td> <Td> License SA 3.0 and the GNU Free Documentation License 1.2 </Td> </Tr> <Tr> <Th> Tracker </Th> <Td> Linux, Unix </Td> <Td> Open Source desktop search tool for Unix / Linux </Td> <Td> GPL v2 </Td> </Tr>

How many types of search engine are there