Timan Rebel presents on HTML5. He discusses how HTML5 aims to simplify HTML and be backwards compatible. It introduces new semantic elements like <header>, <nav>, <article>, and <section>. HTML5 also brings multimedia capabilities through <video> and <audio> elements, as well as access to device sensors. While promising, HTML5 and CSS3 still have open issues regarding codec support and cross-browser compatibility. Overall, HTML5 looks to unify web development standards and support rich content and applications.