Where TrueCrypt left off, VeraCrypt has picked up the baton. (It has the exact same interface, same features with improvements made behind the scenes.)
The TrueCrypt letter specifically said that there “May still be unresolved security issues…” They didn’t say it wasn’t secure. They were quite vague. They were in the middle of an audit and quit before the results came out. VeraCrypt takes the results of the audit and appeared to correct some of the very minor issues. I was impressed by how few they are (i.e., increasing some iterations from a few thousand to hundreds of thousands), and bringing parts of the coding to current standards. They have a FAQ on their website. The transition has been stable for me. – C.S.