If you're looking for a free and open-source alternative to CSP, you might consider:
Available for Windows, macOS, iPad, and Android tablets. This allows you to experience the high-end EX version features without entering any payment information. 3-Month Free Subscription: clip studio paint for free
(If posting on a blog, link to the official Clip Studio Paint download page here). If you're looking for a free and open-source
Want a short social-media caption version? you might consider: Available for Windows