A charter school may be established as a nonclassroom-based independent study program. Enrolling in one of these is a legal option for homeschooling. The charter school is a public school, students are considered public school students, and it receives state tax dollars funding.
Typically, a charter school independent study program (Charter ISP) will provide a fixed amount of funding for parents to choose to spend on approved learning resources. The parents can usually submit for approval vendors they would like to use. Vendors can include book or other educational resource sellers, but also often include businesses offering other things such as a karate or dance studio.
Charter schools may be operated by nonprofit organizations (nearly all of them) or by for-profit businesses (a very small number). They are chartered by a local school district or a county department of education. The charter specifies details about how the school is to be run. The charters are also required to obey various federal and some state educational code. For example, the charter must hire teachers with currently valid California teaching credentials. Students in charters are subject to the same testing requirements as students in regular public schools.
Charter ISPs also different from other public schools especially in that they have much more freedom to offer learning materials outside the CDE-approved lists. Their funding is not based on daily attendance, as is the case for brick and mortar schools, but on evidence of work completed (therefore they require regular submission of work samples).
Charter schools can serve students in the county in which they are chartered or any county that is contiguous to the county in which they are chartered.
The California Department of Education offers a map of the counties of California which allows you to click on a county to see a list of charter schools chartered in that county and it identifies there which ones are nonclassroom-based independent study programs (those highlighted in pink).