Entrecard actually acts like an online business card where you can exchange it with other bloggers online.
How it works?
All members of Entrecard have to put a 125 X 125 Widget on their blogs. Members earn credits by clicking on the Entrecard placed at the different blogs. Therefore, there is a chance that your blog is viewed by the other members. This in turn generate traffic for your blog but bounce rate from Entrecard will be high. This is because the purpose of them visiting your blog could be just to earn credits and not actually for the content of your blog. But at the initial stage of blogging or online business, every single traffic counts because there are chances that they show interest in your blog.
Apart from this, you can also put up your own 125 X 125 ads on other blogs as a form of advertising. However, you need to spend on the credits that you earn.