Trustees of revocable only owe fiduciary duties to the settlor. Beneficiaries have no rights.
Under the UTC, revocable trusts can be amended at any time by any method that manifests clear and convincing evidence of his intent to do so. UTC § 602(c).
Trusts, while often just used in place of a will, can also be used to maintain control of one's property after death. This can allow it to provide for disabled persons or minors, to ensure that it is is slowly, to go to those in the lowest tax brackets, or to ensure to goes to someone else after the first beneficiary's death.
The settlor does not have to understand trust law or even know the term "trust". He just has to manifest intent to create the fiduciary relationship that a trust comprises. E.g., transferring property "for the use and benefit" of another creates a trust.
Ascertainable beneficiaries are not needed for trusts made for charitable purposes. All states also allow pet trusts for pet animals and statutory-purpose trusts for certain other non charitable purposes, like grave maintenance. UTC § 408 & UTC § 409.
A resulting trust is an equitable reversionary interest that arises by operation of law in two cases:
An express trust fails or makes an incomplete disposition
O gives X property in trust to pay the income to A for life, then to A's descendants. A dies without descendants. X becomes trustee of the property for O then. The remainder interest of the trust just results back.
O gives $10,000 in trust to pay $4,000 to A over 5 years. $6,000 reverts to being in trust for O.
One person pays the purchase price for property and causes title to be taken in the name of another who is not a natural object of his bounty
If A buys a farm but puts it in B's name, B becomes a trustee for A.
If A gives B money to buy a farm, B becomes a trustee for A.
If A gives B money to buy a farm or buys him a farm himself but says that the money/farm is a gift, A just owns the farm.
Secret trusts are where the will makes an absolute bequest, without manifested intent to create a trust, but where the beneficiary promised to use the property in a certain way. This promise is then enforceable (creating a constructive trust) to prevent unjust enrichment, and extrinsic evidence is allowed to establish the proof of the promise.