Martin Luther actually believed that some of those who hijacked his ideas were too radical in their beliefs and actions. Luther wholeheartedly believed in peace and was not interested in a violent rebellion of any kind. In 1521, as a reaction to violent protests regarding religion, Luther wrote A Sincere Admonition by Martin Luther to All Christians to Guard Against Insurrection and Rebellion. Here are his words:

Do you know what the Devil thinks when he sees men use violence to propagate the gospel? He sits with folded arms behind the fire of hell, and says with malignant looks and frightful grin: "Ah, how wise these madmen are to play my game! Let them go on; I shall reap the benefit. I delight in it." But when he sees the Word running and contending alone on the battle-field, then he shudders and shakes for fear.

Though his writings had the effect of quelling some violence, radical preachers instigated the German Peasant's Revolt in Luther's name in 1524. He became so angered by their actions that he wrote Against the Murderous, Thieving Hordes of Peasants in 1525, stating:

Therefore let everyone who can, smite, slay, and stab, secretly or openly, remembering that nothing can be more poisonous, hurtful, or devilish than a rebel ... Fine Christians they are! I think there is not a devil left in hell; they have all gone into the peasants. Their raving has gone beyond all measure.

The protestant churches across the world (basically every church you see that isn't Catholic. Lutherin, Baptist, Methodist, Presbyterian, etc) are all descended from the reformed church that Luther created. The intent was never to create a new religion, but to correct the problems they saw within the catholic church at that time.

Their ideas caught on very quick, and they saw them in their lifetimes. Luther's reformed church swept through Germany, and Calvin's through Geneva & the surrounding areas of Switzerland.

Quick note: The Anglican church in England split from the Catholic church at the same time as Luthor/Calvin, but has little to nothing to do with them, so I wouldn't consider it one of the "Protestant" churches

As far as whether or not Calvinism is still around, very much so. Large portions of Calvinism are still present in Baptist and Presbyterian churches.

The entire history is fascinating. R.C.Sproul (a pastor of a reformed church and a historian of the Luthor/Calvin reformation) did a pretty good series on the history of it here. (Fair warning, he's approaching that from the mindset of a Christian who believes 100% what Calvin and Luthor taught, so be aware of his bias)

At first Martin Luther wanted a discussion inside a round of scholars, but they spread his messages fast around. What Martin Luther didn't realized the shortly invented printing technology transported his message fast through the country, which made him to a problem, because he criticized the extended ground for financing the church by paying for redemption.

Martin Luther got reported in Rome and went under the bandwagon of politics. The duke of Saxony supported Martin Luther and several of his theses were misrepresented with purpose and the conflict escalated.

He developed a version of a church controlled by bishops, without the influence of politics, which didn't happened of course. Several dukes and cities decided for their citizens they want to join the better church for their citizens. Most of those churches were under control of the government until the 20th century.

The Danish king was educated at the court of the German emperor and introduced protestantism by force in Denmark and Norway, which gave Denmark the opportunity to seize all property of the catholic church.

Martin Luther itself translated with the Help of Philip Melanchton the bible to a everyday German used in his region, which became later a first standard for German. He was very good into expressing thoughts with this type of German and made from songs from the streets new songs for the Sunday service. His idea only the bible is a reference was the root for reading the bible in families.

The dukes of the different baronies itself used the reformation as a tool to weaken the power of the emperor, which went very bad in the 30 years war after 1618. Without the Swedish King, protestantism would have been eradicated from middle of Europe.

If you're interested in learning what Luther taught, there are many short Lutheran writings summarizing his beliefs. Start with Wikipedia on these topics, but it's easy to go right to the source and read The Augsburg Confession, Christian Liberty and Preface to Romans. Roland Bainton's "Here I Stand" is a terrific introduction to Luther, too.

It may be helpful for you to think of Protestant sects or denominations not as splinter groups, but as perspectives of theology that claim to reach the heart of Christianity in a purer form. Most Christians strive to be Christians, plainly. Protestant sects have more to do with theological movements, nationality, and history that seek to create a stronger Christian identity than with attempts at splitting off and starting new religions.

Concerning the terminology, Lutheranism and Calvinism are two types of theology within Christianity, properly speaking. But a church or church organization that espouses Lutheranism is usually called "Lutheran" in America, but a church that espouses Calvinism is usually called "Reformed." It's confusing, yes. So, Lutheran Churches are Lutheran, but many Presbyterian, Dutch Reformed, and Baptist churches can be considered Reformed (Calvinist).

In Europe, however, most Protestant churches of either Calvinist or Lutheran persuasion are called "evangelical," distinguishing them from the Roman Catholic Church. "Evangelical" implies a focus on the gospel as salvation by faith alone, which was the central teaching of Luther and Calvin.