Which of the following is considered a popular will substitute?

A will substitute is an instrument used to transfer property without going through the probate process. Life insurance is generally classified as a will substitute because the proceeds from the policy are paid directly to the named beneficiaries upon the insured's death, bypassing the decedent's estate. This direct transfer feature makes life insurance a popular option for individuals looking to ensure certain assets are distributed swiftly and privately without the complications that may arise in the probate process.

In contrast, other options listed have different characteristics. Real estate transfer typically involves a deed, which may not necessarily function as a will substitute since it may require probate if not structured properly. Testamentary trusts are established through a valid will and do not avoid probate; instead, they are executed as part of the probate process after the testator's death. Probate assets refer to properties that pass through the probate process, which directly contradicts the concept of a will substitute, as these assets ultimately require the administration of the estate.