Nine year 4-H Alum here, plus University 4-H and Cooperative Extension office too ....
The goal of 4-H is to help students learn how to engage in learning and in the community in an effective way -- it used to be a way to teach new farming techniques to farm kids so their parents would implement them (and new housekeeping techniques, ie safe canning methods). I think that's still somewhat an aspect of the program, but it's grown into more of a leadership and well-rounded program beyond just agriculture.
4-H is going to vary from state to state. In the more rural states, it still has a heavier focus on agriculture/animals but in urban areas there is a greater focus on urban/less agricultural projects. Everywhere, there is some sort of record keeping component, with records due at the end of the year (which coincides with the beginning of the school year). Kids keep records for their projects (costs, outcomes, etc.) as well as a general overall statement of the year too.
Many states have "pocket pets" programs where kids can learn more about and show their unusual pets - snakes, guinea pigs, cats, etc. There are rabbit and poultry projects which are more adaptable to urban areas, and some areas have projects for urban kids interested in large animal livestock (our community has a program with miniature horses for this). And of course, there's the dog project. If you're in a rural area, there are horse projects, livestock projects, breeding animal projects, and more.
In terms of 'indoor exhibit' projects, the standards are sewing, knitting, crocheting, quilting, cooking, baking (cake decorating), canning, photography, electronics, robotics, aeronautics, shooting sports, entomology, wildlife, range management, gardening, computers, woodwork, leathercraft, child development/'babysitting', leadership, etc.
There are also self-determined projects, where kids can develop a project (for a year or for long-term) on something they're interested in. I saw a great one a few years ago, where a kid started with refurbishing old lawn tractors and was moving on to rebuilding automobiles as a teen. Very cool.
4-H members have a monthly club meeting of kids of all ages, 9-18. Meetings are run by the kids, kids plan what they're going to do, they learn parliamentary procedure and officer/committee responsibilities. Parents are obviously involved. Clubs usually have at least one civic project that they do each year (help clean a highway, or visit elderly at the resthome, or whatever). Most clubs require each member to do a speech and demonstration for the club during the year, usually related to their projects; and some counties have this as a county competition and a statewide competition as well. Many counties have a camp in the summer, sometimes combined with other counties but in larger counties, it might be just the 9-11 year olds, then just the 12-14 year olds, etc.
Some (most) states have a county and state fair during the summer where students exhibit their projects. If you place high at the county level, then you can compete at the state level, whether you're 19 or 9. The county fairs have interview judging (kid sits with judges and discusses the project, what s/he learned, plans for next year, etc.). Parents can't participate in the interview judging. There are usually county and state-wide fashion reviews for kids who sew or do the buymanship project to model their clothes and talk about them with the judges too.
As kids get older, they have the opportunity to join Junior Leaders (13 and older) who work on a county level to plan events and coordinate beyond the county level with other teens. Also, once kids are 14, they are usually eligible to compete in regional and state-wide competitions, and to attend national events too. I was lucky to attend one of the last National 4-H Congresses; they canceled it awhile ago but I think they're starting it up again. The teen years are really great in 4-H.
Kids learn record keeping, time management, how to plan ahead, how to communicate effectively with others, interview skills .... I think 4-H did a great job of preparing me for life beyond school. It gave me an edge over other kids while applying for scholarships and doing interviews.
Some of my closest friends from my childhood/youth are friends I made through 4-H.
I didn't mention Cloverbuds - I think this is even more subject to local differences, but usually it's kids 5-8 years of age. They usually meet once a month, do a fun crafty educational project. My sister is the Cloverbud leader where she lives; she's had the kids sew fleece lap quilts for the local nursing home, they've made bread together, done field trips, had a Christmas cookie exchange, etc. She tries to have an educational or civic component to each activity but I think for the kids, they're just fun.
My dd1 starts Cloverbuds here this year - here, it's junior leaders who run Cloverbuds and it's more social/crafty.
Leaders have to have a full back-ground check (I didn't mention that - usually parents help kids with their projects, but there are also projects leaders who hold meetings and trainings and practices for the kids too - they had a great Sewing Camp here for the sewing kids this past year, for instance).
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