Intrinio provides income statements, balance sheets, and statement of cashflows going back 10 years, in addition to stock prices and valuation ratios, via API. You can programmatically query the API to pull the data into your app.
Some examples:
https://api.intrinio.com/financials/standardized?identifier=YUM&statement=income_statement&fiscal_period=Q2&fiscal_year=2015
This grabs YUM's income statement from Q2, 2015.
https://api.intrinio.com/companies?latest_filing_date=2017-03-06
That shows all companies with a new filing date on or after 2017-03-06, which is useful for determining which fundamentals need to be updated.
https://api.intrinio.com/data_point?ticker=AAPL,MSFT&item=pricetoearnings
That pulls the current price to earnings ratio for Apple and Microsoft. You could swap out last_price to get the current stock price.
https://api.intrinio.com/data_point?ticker=$FEDFUNDS&item=level
This call returns the current federal funds interest rate from the federal reserve.
https://api.intrinio.com/prices?ticker=AAPL
That returns the price history for AAPL.
Intrinio gives away 500 daily API calls to any developer.