When Google killed off its RSS reader a vacuum opened up in the app fabric. Of all of the attempts to fill its place, Feedly is probably the most successful. Now it has an API and you can create custom RSS readers.
Feedly, the service the mopped up most of the ex-Google-Reader users, is now making a play for the RSS developers left with nowhere to go. Well perhaps this isn't quite accurate, as Google Reader didn't have an offical API and some reverse engineering was needed. Even Feedly was once a user of the unofficial Google API before it managed to build the infrastructure needed to go it alone.
Feedly seems to be making money. When recently it offered a one-off lifetime subscription for $99.99 it made $500,000 overnight. Even so it needs to keep the cash rolling if only to power the servers. It claims to process more than 30 million feeds per hour - and this seems entirely reasonable.
The new API has been in development for the past six months and it is now publically available. You can use it to build an app that taps into a single user's feeds. Feedly users can organize their feeds into categories and the API presents this as a "personalization graph". What this means is that you also get access to metadata on the way each person is using RSS; not only how they organize data but what they have read and what they haven't. The content can also be accessed as a JSON feed. The whole API is Rest based and can be used from any language capable of making HTTP calls.
There are already a number of apps ready to download including IFTTT (If This Then That), Sprout Social, Mr Reader and so on for a range of platforms including iOS, Android, Windows etc. These were developed by "trusted" Feedly partners.
To access the API you simply have to sign-up to the Feedly Cloud Developer Program giving name, email and optionally a short outline of your project. Then you will get a client id and a client secret that is used to authenticate your access to the sandbox. The sandbox provides a sample of about 1000 feeds for you to work with. To access a real Feedly account the user has to provide credentials using OAuth 2. 0.
This is a good opportunity if you have any good ideas to process or present RSS feeds in a new way or if you simply want to gather information from what readers are reading. Feedly isn't likely to do a Google on you and shut up shop just because the number of users isn't as huge as Gmail.
What isn't clear is what financial reward Feedly expects in the long term. At the moment it seems that there is no charge and no usage quotas. There might be rate limiting in operation - there is certainly such a facility built into the API. However, Feedly surely isn't going to be as generous as Google in the long run. Feedly is a commercial operation and most likely will charge if your app becomes popular. The big problem here is guessing how much.