Open Source has been the basis of Android and runs the biggest sites on the net. So what about Open Source apps?
I was looking around for Open Source apps and I found a few sites, that collect them. There is already a short list with apps on Wikipedia. The web catalogue of Android Open Source has about 500 apps to download.
F-droid, the Android FOSS Repository is an easily-installable catalogue of Free and Open Source software. They have about 750 apps that you can download after you install their catalogue. You can either download the catalogue as an apk from the website, or browse the site to download apps their. You need to have set the ‘allow install from unknown sources’ option on your Android device.