Here is part of the email that he sent me:
In early April I finished the first draft of my 12th which is a college upper-division math book (Life of Fred: Linear Algebra). It was 13 months in the writing. It was a kind of experiment to see if Fred could be incorporated into a more theoretical setting which included such things as homomorphisms of vector spaces.
Then I've gotten "back to work" at the homeschooling level. The tentative title is Life of Fred: Pre-Algebra 1 and Biology. It should "write" a lot quicker than that upper-division LOF:LA book. I estimate that it will be ready by the end of summer. I don't tell the kids, but the math will be 80% review of LOF: Fractions and LOF: Decimals and Percents with the problems often coming from a biological context.
Then, tentatively, Life of Fred: Pre-Algebra 2: Economics, in which Fred will take arithmetic into the business world. And Life of Fred: Pre-Algebra 3: Physics.
Sounds great, but maybe too late for my son, we will see.