This primer is aimed at Pauper EDH, but mostly focuses on commons, so it should also be somewhat applicable to Pauper.
Freed from the Real and other similar effects that allow for repeated untapping of a creature create infinite mana loops with many interchangeable pieces. The combo is available to decks using both blue and green, but has a few potential enablers and outlets in other colors, as well.
The basics are that you'll need an untapper like Freed from the Real, a mana producer that will be repeatedly untapped to produce infinite mana, and an outlet that will turn your mana into a win. Some mana producers will need enablers to allow them to create additional mana before they can go infinite. For example, Freed from the Real combined with Blossom Dryad will not produce infinite mana unless you have a land that produces more than one mana, like with Simic Growth Chamber or a land enchanted with Gift of Paradise.
As was mentioned earlier, requiring multiple colors (or lacking interchangeability when in mono-blue) is why this combo is seen less often than the infamous drake combo. However, there are two main upsides of this combo. The first is that with extra mana, it can respond to instant speed enchantment removal by simply untapping again before the removal resolves and continuing the infinite mana loop. The second is that the combination of infinite untaps and infinite mana give you an very large number of outlets when compared with other infinite mana combos.
For the list of outlets, I have only included single cards that are a self-contained win condition or single cards that let you draw your library to find another win condition. An example of an outlet that is not listed because it requires two cards would be Groundskeeper + Flame Jab.
To interact with the combo, there are two main opportunities. First, when the untapper is cast, it can be countered or you can destroy the target. Second is when the outlet is cast. It can be countered, or if it is something like an aura, then the targeted creature can be destroyed.
This combo is notoriously powerful with Ley Weaver and Lore Weaver, since it allows for a one card combo with the commanders that wins the game. I've included a notable commanders section for several other commanders that have the ability to fill the mana producer or outlet role in this combo.