I believe you're thinking of BrowseInApp by Alan Yip. Is that the tweak? I used to LOVE that tweak. Sadly, he no longer updates it. He released ProWidgets for iOS 7 last year and that replaced BrowseInApp. While ProWidgets is certainly impressive, I didn't buy it because I don't need all that extra stuff. I just want a simple window to open when I click a link to check something out real quick and then go back to the main app I am using. Oh well, luckily the new devices are so fast it doesn't really matter. Man I forgot about BrowseInApp. I miss that tweak!
Anyways, not sure that's the tweak you're thinking of. If it's not, I'd love to know what it is because I'd love that functionality if it were available and lightweight.