Facebook widget tracker Appaholic has been acquired by Altura Ventures. A good write up of the features of Appaholic can be found at Inside Facebook:
“Using Appaholic, you can create accurate models of your application’s growth. If you’re growing too slowly, you need to know so you can fix the problems that are keeping users away. If you’re growing too fast, you need to know so you can move the application to a host that can accommodate it. You’d also like to be able to set goals and know if you’re on track. Will I have 1.2 million users within two weeks?”