This is Mazačka, Prague track lubrication tram popular among transit fans. It would run on a special route across all major tracks every day. Now that 15T trams are getting fitted with lubrication units, it would have become obsolete but they fitted it with a tank and sprinkler to irrigate green corridors, giving it a purpose and placating the fans. It no longer runs every day but there is a schedule and webcam available. There are probably more purposes to it, I think air quality monitoring, leaf removal, track quality control and of course exclusive rides for fans.