If you ever performed a factory reset or somehow lost all of your data from your Windows Phone (maybe even upgraded to a new device) you know it’s a bit annoying to reinstall all of your applications. You don’t necessarily need to re-purchase content but you sure have to find the apps again and push that install button.
Reinstaller tries to address this issue. It will require you to log into your account (which for whatever reason does not work on my phone at the moment) after which it will fetch all the apps that are tied to your account. From the Install section of the application you can then re-download and apply all the applications that you had on your previous installation.
Of course, the equivalent to this is going to the Marketplace on your computer and logging in, followed by going to your Account (Zune also lists the applications purchased). Find Reinstaller at the source link below and let us know if it works for you (at least until Microsoft comes up with an official automated way to do this — and maybe even keep game scores, achievements).