Pluralistic Universalism asserts there is no evidence that any one religion is unique or superior to others and none have more, better, or easier knowledge of/access to God or Ultimate Reality. Therefore it doesn't really matter what spiritual path you follow because there is no conclusive evidence in favor of one religion being 'right' - there is at least some validity and truth in almost all religions and philosophies. All that matters is that you are "sincere", and have some version of God in there somewhere.
Advocates of this position often appeal to the common factors between religions, most especially the fact that many of them have a similar moral code and often produce positive moral changes in their followers.
Besides which a large percentage of the population, cheerfully confusing democracy and truth, has run with the idea that tolerance of all religions means that one has to accept all religions as being equally valid paths to God. What they do not take into account is that all the major religions contradict each other on the most vital of issues. It is also tragically true that few of those who believe that all spiritual beliefs are valid paths to God seem to have made an in depth study of various religions to see if their claims are based on fact, or fairy dust. See Religious Pluralism
Exclusivism asserts that only one way is true and all others are in error. To put it another way - you have believe in Jesus in order to benefit from what He did. See Salvation As said by the late Calvin Shenk a veteran missionary in Africa and who taught at Eastern Mennonite University from 1976-2001 said the following,
Christ did not come just to make a contribution to the religious storehouse of knowledge. The revelation which he brought is the ultimate standard. Since in Christ alone is salvation and truth, many religious paths do not adequately reflect the way of God and do not lead to truth and life. Jesus is not, therefore, just the greatest lord among other lords. There is no other lord besides him. 
Many, if not most, non-Christians assume that Christianity is a "blind faith"... that Christians ignore reality and have unquestioning loyalty to an absolute belief system without proof or evidence. In fact, that they believe contrary to all evidence and facts. Much to the contrary, the Christian faith is a commitment based on evidence. The Judeo-Christian faith consistently stresses the importance of truth, and makes appeal to evidence to support it's truth claims.
There is far more evidence in favor of the Bible being true, than there is for any of the other 'holy books' like the Qur’an, the Bhagavad-Gita, the writings of Confucius, or the Book of Mormon. This evidence includes its humanly impossible authorship, its candor about the faults and failings of it's main characters, its fulfilled prophecy, and its archaeological and scientific accuracy... none of which are seen in the books of other religions.
Besides which, far from being outdated, out of touch, and largely irrelevant to modern society, the Kingdom of God Jesus was sent to earth to proclaim (No, His main message wasn't about 'love') is exactly the utopian world most men and women can only dream of.
See Choose Life That You Might Live.
Christian Universalism holds that Jesus is the only way - His death on the cross provides atonement for all sins and redemption for humanity. However, contrary to traditional belief, universalists believe that everyone will be saved through faith in Christ regardless of whether or not they repent of their sins, trust in Christ for salvation etc. If they die without doing these things some say that they will be given the opportunity to accept Christ on the 'other side'. If they do, they will be forgiven their sins and granted entry into eternal life in God's kingdom, perhaps after a period of punishment.
Many in the Universalist camp believe that all human beings are already reconciled to God even if they are unaware of it. Therefore the job of the preacher and the missionary is to tell people they are already saved. In other words, all of mankind is going to be saved by a superior power - whether or not they wish to be.
What we need to ask ourselves whether Christian Universalism is Biblical or whether it can be assigned to the wishful thinking category. See Universalism
Inclusivism is a sort of middle ground between Exclusivism and Pluralism. It asserts that while one set of beliefs is absolutely true, there is truth to be found in others.
Inclusivists also hold to the idea that it is possible to worship the true God without explicitly knowing it and you don't necessarily have to believe in Jesus to benefit from what He did.
Some believe that God judges all people based on their response to natural revelation. He condemns people who violate natural laws as they understand them but shows mercy forgiving those who have lived up to whatever light they had.
For when Gentiles who do not have the Law do instinctively the things of the Law, these, not having the Law, are a law to themselves, in that they show the work of the Law written in their hearts, their conscience bearing witness and their thoughts alternately accusing or else defending them, (Romans 2:14-15 NASB)
Although there is no salvation outside of Jesus Christ, God will extend His mercy to many who lead moral lives but may have incomplete or no knowledge of Him in this present life. One example used is the conversation between Jesus and the Samaritan woman when He told her "You worship what you do not know; we worship what we know, for salvation is from the Jews," (John 4:22)
Inclusivism has been around for centuries but perhaps one of the reasons it has recently become so popular is the need to make Christianity a more "user friendly" religion. God's wrath and justice, the exclusivity of Christ, and the doctrine of eternal punishment are all hard pills to swallow.
See What and Where is Hell?
Does The Bible Really Teach that Sinners are Condemned to Eternal Punishment?
Unfortunately, among other difficulties, inclusivists have to somehow defend the idea that God has changed. In the Old Testament God repeatedly makes very clear that He detests idol worship and warns the Israelis not to make a covenant with idol worshipers lest it be a snare to them. He commands them to destroy their altars and cut down their wooden images (Exodus 34: 12-17) and warns them that He is a jealous God.. He likens idol worship to playing the harlot. The book of Kings repeatedly talks about the high places where they burned incense which is described as "wicked things which provoked the Lord to anger" (2 Kings 17) which finally caused God to "remove them from His sight".
Neither is the New Testament deficient in it's condemnation of idols. Idol worship is described as demonical (1 Corinthians 10: 20-23), defiling (2 Corinthians 17-18), enslaving (Galatians 4:8-9), abominable (1 Peter 4:3). Additionally Revelation 9:20 speaks of men who, even after many plagues did not repent of their worship of demons and idols. Revelation 22:15 makes it very clear that idolators have no part in the New Jerusalem but are "outside". (Revelation 21:8 includes both idolators and unbelievers' in those that have their part in the lake of fire. [Also See Idol Worship... The Spirits Behind The Idols
The Jews in the Old Testament found forgiveness for their sins through the animal sacrifices, which was a temporary measure until the final sacrifice of the Lamb without blemish. The Bible says nothing about the surrounding idol worshipping nations being forgiven through these animal sacrifices, but inclusivists would have us believe that present day idol worshipers are automatically saved through Jesus' death, which, if it were true, would lead us the to the obvious conclusion that God has changed.
 Calvin Shenk. Who Do You Say That I Am? Wipf & Stock Pub (April 7, 2006) Pg. 35