As far as Islam is concerned, you might not have asked this but its an interesting contrast.
A person salvation depends on the time and place that they were born into. Did they belief in the Prophet of that time?
If they did then they have a good chance.
Who is the Prophet of this time?
The final Prophet of this time is Muhammad (peace and blessings of God be upon him). So did they hear about Islam? Did they no get a chance? If they studied IIslam and had a chance to meet good Muslims and rejected it; then this person has nothing to complain about.
On the other hand people who haven't heard about Islam and never had a chance to study it, nor met any true Muslims.
Then he will have a last chance with God/Allah.