Whit Jackson made one which appears to become made working with HTML/Javascript (GitHub url). He also had a website in which you could generate the addresses customer side, but it seems for being down now. BTC addresses use Base58 (like Base64 but without very similar character: IOl0+/) and should get https://ethereumvanityaddressgene65320.jts-blog.com/29087384/rare-trx-fundamentals-explained