This is a Google Scribe. It's Google lab service. It offers a suggestion feature for English. So I can save types and prevent typos.
What it makes so good is, that I can use it in any input form by using a bookmarklet. For example, I am writing this sentence enabling Google Scribe.
Although I like the idea of this feature, it's rather annoying for now. Because it's a bit slow so it can't keep up with my typing. I type some words, and seconds later, it shows candidates. Too late.