I can find plagiarism checkers, but these tend to be looking for whether the texts have a common source, rather than a common author. (If I write two texts, one about soft fruit and one about deckchairs, they are liable to pass a plagiarism test, but should still have enough in common for someone to be able to say that the same person wrote both...)
This entry was originally posted at http://lovingboth.dreamwidth.org/469880.html, because despite having a permanent account, I have had enough of LJ's current owners trying to be evil. Please comment there using OpenID - have and if you have an LJ account, you can use it for your OpenID account. Or just join Dreamwidth! It only took a couple of minutes to copy all my entries here to there.