RuneScape – Multi-player Roll-playing Adventure Game.
Make sure to click through from here to get an EXP boost and a starter pack when you create an account.
Take part in an adventure working your way through quests, team activities, and level building to work your way through the ranks.
RuneScape has a vast Free-To-Play (FTP) world that gets even larger if you choose to become a Pay-To-Play (PTP) member. If you choose to become a member, not only does the explorable world grow by 20x, but you get access to more quests, items, many more perks to list here.
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Pogo has a lot of games to offer, some free and some that come with only the paid subscription. If you are playing the free games and would like to play the member games for a few days then join a channel with a lot of people in it and ask for a member to give you a free 5 day pass. If you are lucky then you can get you up to 2 weeks free for signing up. That is if Pogo is running that offer.
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Neopets is an online gaming site like Pogo but is aimed toward the younger crowd. They do have many activities and games for older kids, and some adults too.