Fallout 3 hidden weapons?

I heard that there is an alien blaster i found one and was wondering if there are more hidden weapons like that.. i found a board of education up in these cliffs with a super mutant master... i looked on youtube some and saw a person grab like an experimental fat man that fired many nukes at once.. was wondering if you knew where to find it or if it was a mod... also saw a fire hydrant like what the super mutant behemoth used i think it was a mod but i wasn't sure. If there is anymore i am missing please tell me and give me the location of it i need some better weapons.. also i heard that at old olney there was experimental armour.. is this true? if so can you give me more details about what it gives?