IN total, as tramways are my prime interest in transport, around 333 systems in 48 countries. In Paraguay and Vietnam abolished since. In Israel, Emirates, Denmark, Luxembourg, Ireland, Argentina, Morocco newly started (even if in some they had older systems closed down). Will not list them all- except for Byelorus and Russia all systems n Europe, and nearly all in the other continents. It remains debatable for some if its tram or metro or more likely in between light rail. I follow the list the german mag Blickpunkt Strassenbahn publishes every 10 yrs. or so. And the Douglas, IoM, horse drawn one- not listed, have been onto it! Around 15 systems have been withdrawn after my visits.
Never been in these countries which now have tramways: Brasil, Bolivia, Equador, Uzbekistan, Algeria. Will likely also not happen anymore.
Have not visited all systems operating during my visits there: again BY and RU (which still was SU then).
And they opened a new tram after my last visit there: Mauritius, plus also like Australia, Canada, USA, China, Japan where I did all existing ones on last visit there. Taiwan is also on this personal list-but visit planned for next week- 2 systems to add (in Taipei as 2 routes separated-like f.e. also in Barcelona and Kaohsiung).
A friend of my has reached the 400 mark-he joined many of the Blickpunkt tours to nearly all Russky systems when these were organised pre 2000.
500 is probably only reachable for those who are that old to have been on many UK/USA systems when still running and then also the East-Eur, communist former world. Perhaps the LRTA keeps a list for that?