This is a database of all the installed applications in the macOS that can be queried to get information about each installed application such as URL schemes it support and MIME types.
/usr/libexec/lsd is the brain of the database. It provides several XPC services like .lsd.installation, .lsd.open, .lsd.openurl, and more. But it also requires some entitlements to applications to be able to use the exposed XPC functionalities, like .launchservices.changedefaulthandler or .launchservices.changeurlschemehandler to change default apps for mime types or url schemes and others.
/System/Library/CoreServices/launchservicesd claims the service com.apple.coreservices.launchservicesd and can be queried to get information about running applications. It can be queried with the system tool /usr/bin/lsappinfo or with lsdtrip.
File Extension & URL scheme app handlers
The following line can be useful to find the applications that can open files depending on the extension:
./swdagetSchemes#Get all the available schemes./swdagetApps#Get all the apps declared./swdagetUTIs#Get all the UTIs./swdagetHandler--URLftp#Get ftp handler
You can also check the extensions supported by an application doing: