voluptuous is back in active development, and I have a plan to merge onctuous improvements to it: https://bitbucket.org/Ludia/onctuous/issue/2/make-list-of-changes-to-submit-upstream
onctuous has unit tests, docs and some extra features.
voluptuous has auto-coerce, which is great when you want to use validators as converters and not type checkers ;-)
For a smooth transition, we could make an onctuous release that’s just a compat shim for voluptuous so that people can continue to import stuff from onctuous, with or without DeprecationWarning. What do you think @Hadrien David @Michel Noel?