Depending on what you're into there's three games that I'm more or less actively playing on. They're all based on the Ares Engine so have full web portal functionality to play via web and client. (I purely play via portal because I find it much less stressful!)
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Crystal Springs - A game where you play an actor starring in a 24/7-esque television show where you play a high school student in the California city of Crystal Springs. Very active, lots of friendly players and ways to get involved in stuff. Also Pacha, the site creator/admin/ST, is fantastic.
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The Network - Another game where you are an actor but this time it's for a place called The Network. You don't have any solid memories of who you were before coming to the Network and the theme rotates every few months. Each show you take on the entirety of your Season character and don't have any memories of anything else until you come back to the Dome - which is the place the Actors live between Seasons.. Now is an excellent time to check it out because the previous season just finished so all the Actors are back in the Dome and the next Season will be starting in a few months or so. Very active with lots of friendly players here too and lots to get involved in if you wish.
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Gray Harbor - Set in the PNW, in Washington, Gray Harbor is a modern supernatural setting. It's fallen from the activity that it used to have but it is starting to gain steam again and there are several dedicated players who are still around and very welcoming. The best way to describe the setting to me is if you like Stephen King, you'll love this. I often like to think of 'It' and even 'The Shining' as good examples. So if you like the idea of having some psychic like abilities and supernatural things messing with you this is it! This is the game that utilizes the Web Portal for Ares the most of the three - in the sense that the time zones are often all spread out so a lot of the scenes are Asynchronous so everyone can participate.