There are no estate or inheritance taxes in most states. Please elaborate on the trusts that avoid federal estate taxes! I used to be a corporate tax attorney, and worked in one of the leading international law firms for estate law, but have never heard of such a thing.
They are called dynasty trusts and the IRS allows shelter for up to only $11.7m per individual. After a google search I see there are many more states that allow them these days.
I think what you're referring to is the exemption from generation-skipping taxes, and subsequent assessments of estate taxation. IIRC, these instruments are still subject to the regular estate tax when they are first set up, which is why they would typically be funded with an amount that is exempt from the estate tax.