You've also got revocable and irrevocable trusts which are important in estate planning. A revocable trust can be altered during the life of the grantor, whereas an irrevocable one cannot be.
It is fairly common for people with significant assets to protect to take out revocable trusts, which become irrevocable upon the death of the grantor. The grantor gets to live on the assets of the trust during his or her lifetime and the rest go to the beneficiaries after death. An advantage here is that a good trust spells out specifically who gets what upon death and there are some "death tax" ramifications that can be somewhat avoided with a solid trust.