From their Kickstarter page
Will Papier support Linux?
Yes! We're leveraging Unity 4 to support the Linux platform. Therefore, the Linux versions officially supported will be limited to those supported by Unity 4. While games exported from Unity will run on most modern Linux desktops, official support will only be provided for 32 or 64-bit Ubuntu Linux, version 10.10 (Maverick Meerkat) or newer, with graphics cards using vendor-supplied drivers.
Note: We have performed successful tests on both the latest Ubuntu and fedora distributions using Unity 4 Linux preview.
They have 13 days left to raise one hundred forty thousand dollars. So far they've raised one fourteenth of that.