App.net is a service that's had its fans and opponents -- it's currently used as a microblogging service, similar to Twitter, where users can share files and updates easily. But unlike Twitter, App.net's had a philosophy of staying away from ads, letting users keep all rights to the content they create, and keeping the API as open as possible. Until now, App.net has only had paid tiers of service, but starting today, they've announced a free tier, meaning users can now join the site and the network for free.
As you might expect, there are some limits. First, you'll need an invite, and the invites are being given out to paid account holders, so it's not exactly an open door just yet. After you sign up, free accounts can only follow a max of 40 people, and will only have access to 500 MB of storage, with a max file size of 10 MB. App.net is also giving away some extra storage space to those who invite users who stick around and follow others, so if you have a paid account already, there's a chance at a bonus if you invite the right people.
If you don't get in on this first run, don't worry -- App.net's devs say they're going to be opening up the process going forward, depending on how it goes. App.net's API is now used by more than 100 third-party apps on a number of different platforms (including apps like Netbot for iPad on iOS), and I expect that number will rise as more and more people join and use the service.
In the past, App.net has gained attention (and accolades) for being a very limited, paid-only network, but offering a freemium tier like this is the next step towards really creating the "movement" and ecosystem the team originally wanted.