Probably a super-hardened (security-wise) OS for an iPod Touch-like "second device" intended for use primarily to arrange illicit assignations.

Very few apps available, all based on zero-knowledge protocols, and no apps that are capable of leaking your real-world identity through ordinary or casual use are allowed.

As a result, just about everyone on Capitol Hill has one of these, so they can't be banned even though they are, as a side-effect, extremely useful to whistleblowers, journalists, activists, dissidents, etc.