First off, TrueCrypt ain't dead. The 7.1a version is as viable as it ever has been. The only question is how well will TC hold up in the future, without ongoing maintenance and enhancement.
Without a shadow of a doubt, the closest alternative is VeraCrypt. It's open source and free. When you check it out, you'll discover (happily, I suspect) it's a nearly identical twin brother (or sister, as the case may be) of TrueCrypt. I recently converted from TC to VC. While tedious and time-consuming, it was remarkably straightforward.
During the past week or so, VeraCrypt was updated, an eventuality not likely to occur with TrueCrypt at this stage of the game.