Getting sick of walled gardens, locked bootloaders and over-managed app stores? (We're looking at you, Amazon.) We've got some good news. A few weeks back we shined a spotlight on the Spark tablet, a Linux-based open source tablet being cobbled together by KDE developer Aaron Seigo. Yesterday, it went up for preorder. Time to whip out those credit cards, Linux lovers! Oh, wait, never mind -- the site doesn't force you to whip out the plastic to land a spot in line for a Spark.