You might be interested in "Code Katas" - small, targeted programming exercises. Check out codewars.com, codekata.com, codekatas.org, etc.
Also check out ACM Competitive Programming problems [0]. They're small projects, usually centered around logic, mathematical calculations, and data processing. If you want a challenge, take one year's problems and try to complete all eight in under five hours without an internet connection (physical reference material allowed).