The Griddle

Slitherlink

Area 51 puzzles may contain slitherlink-style clues. These clues consist of a number in a cell that ondicates the number of fence pieces around that cell.

Corral

Area 51 puzzles may contain corral-style clues. These clues are numbers surrounded by a circle that indicate the number of cells inside the fence that can be traveled to in the straight line up, down, left, and right from the clued cell. (Plus the clued cell itself.) As such, the clued cell must also be contained inside the fence.

Cacti (Wolves, Trees, etc.)

Area 51 puzzles may contain cacti, which clue cells that must be outside the fence when the puzzle is complete. In some fence-building variations, these have been clued by trees or wolves (e.g. Wolves and Sheep variants).

Masyu

Area 51 puzzles may contain masyu-style clues. These clues are filled and unfilled circles found on a grid intersection, as in masyu.

Filled circles must have the fence pass through them with a 90 degree turn on the clued intersection itself, and with straight fence passing through the previous and next intersections along the fence.

Unfilled circles must have the fence pass through them with a straight line on the clued intersection itself, and have a 90 degree turn on one or both of the previous and next intersections along the fence.

Idle Loop/Cathy and Tom Saxton

Friends of the blog Cathy and Tom Saxton have posted some Area 51 puzzles on their puzzle site for various events and occasions.

Krazydad

Friend of the blog Jim Bumgardner a.k.a. Krazydad has created an interactive playable Area 51 web app available to play for free over at his site, as well as generating a plethora as PDFs to save to a tablet or print and solve.