Originally, the DIY ISP movement comes from ISPs which are actually offering access to the Internet. DIY ISPs which did that existed in the beginning of the nineties in many countries. But as commercial ISPs came up and had lower prices, the non-commercial ISPs ceased out of existence. They just closed down, became commercial, or offered different services to remain alive.
Thus, the term ISP is nowadays broadly used. Here, we gather just a few ideas of services an ISP could offer.
You can say: “Hey, I can get $service also for free at example.org” – but that's not what we want to do. Apart from having control over your data and what you do, the other question is about your place in society. Are you a consumer? Somebody, who just consumes what the large providers like Github, Facebook, Youtube, Twitter, Google are offering?
The Internet is not a place where we have to eat what we are served. It was – and it still is – a place where you can bring in your own ideas, where you are free to express yourself. Don't let that drown in the comfort of being a zombie of consumption!
Let's try to roughly group the DIY ISPs out there. You can mainly say there are three types of initiatives (there exist mixtures):
Maybe because of technological interest, or because they want to be able to manage their own services, there are many small providers which are just setting up their own mail- and webservers or other services.
Many rural areas still don't have a good Internet connection. To connect them to the Internet with a fast connection, people set up their own ISPs just for a single small village, often using radio relays.
The classical ISP: Offering access to the Internet. Reselling DSL, providing wifi or setting up fibres.
You most probably won't be able to connect users directly, but you have to be a DSL reseller. In several countries, the owners of networks are legally obligued to rent their cables to resellers. With DSL reselling, you won't be able to serve places which are not connected via DSL, but you will offer those who don't want to go to the large providers an alternative.
In most cases, you won't be able to compete with the DSL prices of large access providers, and fibre or wifi are not applicable. What you can still do to help people having a trusted and secure connection to the Internet is to offer VPN access.
And there are also many people who commonly use unprotected wifis. If they still want a safe link, they have to use a VPN.
The only thing you need for offering VPNs is traffic. VPNs are not attractive if you can use them only half of the time because the amount of traffic is too small.
If you are one of the few happy people to be connected via fibre, or you can dig your own fibre into the soil, you can offer fibre-to-the-home.
Probably the most common model for regional ISPs is to offer Internet via wifi. You don't have to pay for cables, you just set up wifi routers at the right places and sell it to users. Routers are not very expensive, and you just need one good Internet connection where the wifi routers connect to.
You will have much fun setting up the routers, climbing on roofs to set up radio relays, etc. But it is still a lot of work choosing the right places for routers. Especially in cities, large buildings make distributing wifi difficult, but when cooperating with churches etc., you will be able to set up routers at the strangest places.
Dial-Up is maybe the easiest way currently to bring up your own ISP. The problem is: Nobody uses it anymore, except for a fallback. For those having modern DSL connections, they are not even able to use any dial-up connection anymore.
Most of these services seem very trivial. And indeed, they are. Everybody can set up a web server and run a wiki on it. It is important to deliver these services stable and for many people, not just yourself. There is a large number of non-technical people who still don't want to use the large companies, and who are not able to run their own web or mail server.
For those who want to publish information, the web is the place to do so. Free offers are always bound to advertising, are instable, inflexible, or all of these points. There is not much more to say. Just run a web server.
If you run a web server anyway, you could consider also providing some multi-site instances of software commonly used. You will have lots of users running Wordpress or a CMS like Drupal, which have multi-site capabilities. You could just install it, keep it up-to-date, and offer it to your users. This way, you can make it easier for users to run their websites, and you can keep an eye on security yourself – as you are responsible for updates.
Mail is the most important communication in the Internet – full stop. Despite of decades of trying to replace it or declaring it dead, you still have to have an mail address somewhere. After the NSA leaks, you know that all the large free ISPs are not really private. And PGP is not as widely distributed as you would like to have it.
So, running your own mail server is important, and is one of the killer features of your DIY ISP. Mail servers must be local, and people must be able to trust their mail admin. So run a mail server!
For those who want to install software and not share their machine with others, you should offer colocation. Many developers want to have a machine somewhere under their own control. So if you are in a datacenter anyway, why not offer colocation space to other individuals?
There are also many people who would be happy with a virtual server. The costs for virtual servers are not that low that you would have problems to compete with the large ones. Just the initial costs for a server running VMs would be costly.
XMPP/Jabber is an important instant messaging protocol, used by millions of users, often without their own knowledge. There are several free Jabber servers like jabber.org or jabber.ccc.de. But as the free ones sometimes have scaling problems or are instable, having a more distributed network would be welcome. This way, you can also keep control over your communication (which will usually run over the server) or private data like the contact list.
You will get many requests by activist organisations. They are the ones which have more organisation than the usual private-customer-oriented providers can offer, and as activists tend to care for what services they use, DIY ISPs are a good partner.
Even in 2014, mailing lists are an important communication channel for many issues. There are few better ways for private communication via the Internet. Or for public communication without anybody having to register with private data. Or for work-sharing, like ticketing systems.
Many people want a machine where they can always connect to, e.g. to run an IRC client which is always online, or to have an online editor. Having a shared machine where many people can connect to via SSH is a good service. There are also commercial providers exclusively selling SSH accounts, so why not offer that as well?
Open Source activists need infrastructure. And many of them also prefer having autonomous solutions. Hosting repositories is very easy with tools like Gitolite or Fossil. As you might need repositories for yourself anyway (versioning documentation or scripts for servers), you might consider offering it to users as well.
Your potential members are also often Open Source people, or at least people who mind using Open Source software. So you should try to please them as best as possible.
Many people use smartphones nowadays. The problem is that they always want to synchronise with Google or Apple. But you can also run your own synchronisation service with Horde or Zarafa, such that Google does not need to have your phone book.