Duel Arena (Safe). Just as the name states Duel Arena lets players battle against each opponents. It also offers specific rules that RS gold can be set up to add spice to the game (like taking gold coins). This is available to both players as well as free for adventurers.
Clan Wars (Safe). Lets two players from opposing Friend Chats to fight against eachother. There isn't any reward for this kind of activity... perhaps, but not much glory.
The Last Man Standing (Either Safe or Dangerous depending on the mode). It is in the Castle Wars area players can chat with NPC Lisa who can sign them up for LMS. It is essentially an online battleground game that is implemented in RuneScape. Rules are basically the same as in other battleground games . Players are teleported to the islands which is where they hunt for equipment and battle one another. The game is over when the only buy Runescape gold remaining player is present on the island. There is a reward of 1.5mil for first place and 500k for second when you play in competitive mode.