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Linux-libre is a modified Linux kernel created by the FSF Latin America. It removes all non-free components and binary blobs of the Linux kernel. It officially joined the GNU project in early 2012. While the modified kernel seems to be distributed by FSF Latin America, Linux-Libre is actually a set of deblob scripts.
Due to proprietary drivers being removed from Linux-Libre, hardware compatibility may vary based on free drivers being available for the hardware you use. The Free Software Foundation maintains H-Node, a database of hardware compatibility tests and their results. The H-Node database is useful for determining the compatibility of your hardware with Linux-Libre and also to find compatible hardware.
Usage by distros
By default, Most (if not all) FSF-endorsed distros have Linux-libre as their default kernel. However, some distros such as Arch Linux has Linux-libre in the AUR. Gentoo has an option to deblob your kernel when you build it. Debian, while doesn't use Linux-libre, the kernel is deblobbed by default, making it somewhat similar to Linux-libre.