The boomerang is actually fat eights. you send one to 35 people and they use your fabric plus their own fabric make you a block and return it. At the end of the swap you should have 35 blocks with your fabric in it. all 12.5 inch blocks.
The funky chicken and the funky houses. You make a block in any size divisible by 3 plus seam allowance. You make 6 of the same blocks but you can make as many sets as you want. Some you get one of your own blocks back and some you don't.
If you check the first post of the swap topic there is usually all the instructions and you can click the activity page link and see how many signed up.
The siggy swap was made with 3.5 inch blocks all with a white center and any fabric on the ends. It was signed with name, board name, city and state. You could make as many as you wanted. Then they were all swapped out by several people and returned to senders. you pay postage both ways.
Swaps are fun but can be expensive and time consuming so be sure you can make the commitment before you sign up.