fTelnet (https://www.ftelnet.ca) is a browser-based terminal client.  The author just released some changes I submitted and it's working great for me on my BBS atari.electric-estates.com if you want to see it. BBS is a work in progress but shows off the beautiful Atari characters in the browser!
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For BBS Sysops, use  the wizard on the site and select Atari emulation.  If your  changing you current config to its just   Options.Emulation = 'Atari';
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Been a long time coming... fTelnet Atascii is active on this websites home page.