A lengthy "Test Yourself" section helps you remember the original colonies, the many wars, and why we revere the Rev. Dr. Martin Luther King Jr. and Susan B. Anthony.
United States History, by MTC Apps for Android devices, is free (it has advertising support) and has a home page that organizes topics under headings that include the Constitution, important dates, documents, and speeches. A U.S. timeline is searchable, with hundreds of entries starting with Aug. 3, 1492, when Columbus set sail and headed west.
The Federalist Papers section has the full text of the famous public-relations arguments by Alexander Hamilton, John Jay, and James Madison on behalf of the Constitution.
A "Did You know?" space at the bottom of the home screen displays random history entries, such as one-paragraph descriptions of Ulysses S. Grant, Barack Obama, and the Zamboni machine (invented in California).
An app called iUSA, from USAInteractive, is 99 cents for iPhone. It attempts to organize thousands of Wikipedia entries and government Web pages into a U.S. history guide. Nice try, but choppy to explore. Navigation help is a row of icons at the bottom of the screen for history, the White House, Congress, and government.
In the history area, you choose a list either of the states or of the presidents. That's all, though once you get to a Wikipedia page, you can search more widely.
AP U.S. History, from Simple Tree L.L.C., is free for iPhone. The advertising-supported app is billed as a study aid, but it has no official connection to the advanced-placement tests by the College Entrance Examination Board.
The app makes for a sketchy review of America from its founding, with no narrative history. A search for the inconclusive War of 1812 produced three short entries: on the Battle of Tippecanoe, the Hartford Convention, and the Treaty of Ghent.
Simple Tree also has U.S. and World history "flash card" apps, costing several dollars each, for Android as well as Apple devices.
Contact Reid Kanaley at 215-854-5114, email@example.com or @ReidKan on Twitter.