Sébastien Lachance is a Windows Phone developer who (alongside Vincent Gosselin) is behind DualShot. The app, which we're covered in the past, is a neat photography solution that's a replicate of the popular Frontback app on iOS. Lachance has shared on his personal blog how they've managed to accumulate 100,000 downloads in just 20 days.
It's worth noting that DualShot is exclusively available on windows Phone 8 hardware, and can only work with smartphones with two cameras (front and rear). Even though the developers have missed out on the Lumia 520 (a super popular Windows Phone), they've still scored the high download count.
Launching on September 16th, the number of downloads for DualShot surpassed 100,000 on October 15th (100,000 was accumulated between September 26th and October 15th).
It's an interesting read, with data for markets and information on channels used by the developers to get DualShot out in the community with as much exposure as possible. If you haven't already done so, download DualShot (free) from the Windows Phone Store (QR code below). Read through the full blog post over on dotnetapp.