If you don't already have a Guest Account at the NEHGS website, AmericanAncestors.org, you'll need to set one up (here). It's simple enough and free. Guest access automatically includes access to a different set of 20-odd useful databases, so it's worth setting up, anyway.
In addition to the 32 databases included in the current free access offer, researchers will find a host of support information from the Society about probate records and their use in family history research. There's a webinar by probate expert David Allen Lambert, as well as videos on how to search for New York, New England and Massachusetts probate collections, plus written features providing guidance on finding these records and how to get copies of documents.
Free access to the probate collection will continue until Tuesday 25 April.