The only one I have experience with is the Seishun 18. It is available at decent sized JR stations, and it works for local trains. No shinkansen, not even the faster, nicer regular trains. 1 person can travel all day for each stamp put on the ticket. So 5 people could all share 1 ticket, if it were stamped with the same date 5 times. Or 1 person could use it for 5 days, which don't need to be consecutive. You can use it for 1 day, spend several days there looking around, and then use it again for a day to travel further on or back home. Most passes require consecutive days, so this is a nice feature. The ticket is only sold during holidays though, and is valid for that holiday break. You must use it up by the end of that vacation period. So if you buy an 18 kippu for winter break, you need to use it up by the end or else any remaining days are wasted. Here's more info and the dates when they are sold and valid:
Seishun Juhachi Kippu (Seishun 18 Kippu)