Greg Nuckols released 28 program variations through his site, Stronger by Science. While these programs were released for free, I strongly recommend you check out The Art & Science of Lifting and the free lifting guides he authored. See also: Greg Nuckols High Frequency Program (free spreadsheet).
Are There Really 28 Programs?
Wow! 28 programs? Why so many?
If you thought this, don’t worry – it’s not as overwhelming as it seems.
Each of the programs outlined are for squat, bench, or deadlift only and are meant to be used together.
From there, each lift has a beginner, intermediate, and advanced variation.
Finally, each lift and proficiency level has 1x, 2x, and 3x weekly variations.
So, (3 lifts)*(3 skill levels)*(3 frequencies) = 27 programs
You get to 28 programs because there are actually four variations of the 3x weekly deadlift program: beginner, low volume, medium volume, and high volume.
About the Programs
Because there are so many options, a lifter is able to determine what level they are at, how many times they want to perform each lift, and move on from there.
Every program runs on a 4 week cycle, with the lifter testing their 1RM after each cycle. Intermediate and advanced cycles start bringing in variations of the main lift (e.g. programming in a front squat as a variation to the back squat), while the beginner programs stick more closely to the big three lifts in the interest of specificity and learning the movement.
28 Programs Google Spreadsheet