I know that there is plenty of prewar technology hanging around the wasteland but what about all of this post war tech i keep hearing about? Who made it and what is it?

Post War tech... As in advanced tech? Well that would be the Enclave. The guys behind Advanced Power Armour and Vertibirds. Vertibirds were of Pre-War design but the Enclave actually built them.

Then I guess there is the Institute in the Commonwealth that are producing really advanced androids.

We have the Gun Runners and Van Graffs making new weapons of Pre-War designs.