Jenny Morris at Faith & Good Works has created some of her own unit studies, and she has also compiled a list of more than 100 free unit studies, most of which are available from other websites. These unit studies vary in their intended audiences from preschool through high school. These are short-term unit studies that are narrowly focused rather than complete courses. You can use them alongside other curricula to go deeper on particular topics, or you can use them to take a break from whatever else you are doing.
The unit study links are organized under the headings Famous People, Fine Arts, Faith-Based, Science-Based, Human Anatomy, Social Studies-Based, Book or Movie Based, Author, and Seasonal and Holiday.
Morris includes links to her own unit studies, which tend to follow a consistent format. The other unit studies are on many different sites, so they vary greatly in their design. Many of those sites are supported by ads, so you will sometimes have to deal with annoying pop-ups. (Jenny’s own site has affiliate links but no outside advertisements for unrelated products.)
Since I describe Morris' own unit studies in a separate review, in this review I'll describe two distinctly different unit studies from other sites that are on her list to give you an idea of what's available.
Morris lists a study "Fall Fun for Preschool" that takes you to an article titled "Make The Most Of Fall Preschool With These Simplistic Activities" at Grace, Grow & Edify. This article describes a collection of activities that involve picture books, crafts, and a nature walk.
The article recommends letting preschoolers work on hands-on activities while you read one or more of the four recommended books. It includes printable templates for leaves, pumpkins, apples, and an acorn. The nature walk is used for collecting leaves and seeds that match those on an image—shapes similar to an oak leaf, a maple leaf, and a few other common shapes that you should be able to match in many areas of the country. (Children are supposed to try to find leaves and seeds that match those on the image, so it's sort of a scavenger hunt.) You can click on a link that shows how to do a leaf rubbing for art. There's a printable image of a bare tree for children to decorate with leaves--the article suggests a number of ways they might do this.
To get all of the printables in an easy-to-use pack, you need to subscribe to the site's email list. You should be able to print most of the templates individually, but it won't be simple unless you subscribe.
The “Memorial Day Unit Study” at Year Round Homeschooling with Misty Leask should be good for students in grades five through twelve, although there are links to short videos that are usable with younger children. The website has quite a bit of information to read about the background of Memorial Day, and there are six links to brief videos. Some links are definitely for older students and adults while just a few are for younger children. You could have older students read through the material and watch the appropriate videos, and have younger children only watch the few videos that explain Memorial Day on their level.
Putting together a list of unit studies available on other sites presents a host of problems, some of which I encountered in the process of writing up this review. (A unit study I intended to feature was no longer accessible.) The quality of the content can be very uneven. Sites can disappear, and some website owners don't keep links up to date. Objectionable ads or content might appear. And material might become out of date. Morris cannot guarantee that you won't run into these problems, so be aware, and definitely scope things out before having your children work on these other websites.
Unit studies like these are easier to use as a major part of your curriculum in preschool through second grade where homeschoolers generally have more flexibility regarding what they are covering outside of math and language arts. They will generally work best as supplements to your curriculum with older students.