Basically, an "on fire" status for players who have made contact with lava or other flammable sources.
This is a very simple concept that is surprisingly not default. Fire would obviously be extinguished by water and water bricks. Should also probably include an event that sets players on fire and extinguishes them. This would also save add-on developers the trouble of creating their own separate burning effects and simply use the default. Two examples are Iban's and Bushido's molotov roostertails.
Other side notes include the possibility of healing items such as the medpack or pill extinguishing you and how explosions would come into play. I know someone made a script where explosions had a chance to set you on fire but I don't think that would be necessary (would also get annoying). There's not much else to say, as I stated this is pretty simple and self-explanatory.
