There are a number of classes, archetypes, and so on, which grant you some kind of pool, where you can spend a point from it to imbue your weapon with extra power in the form of enhancement bonuses which stack with the weapon, and can be spent as weapon properties as well. What I cant find anywhere is if this works like a proper magic weapon when overcoming DR, or if it works like the spell greater magic weapon and only overcomes DR magic. I know that this would change for every class which grants the ability, so here are the sources I have come across which grant it.
Magus - Arcane Pool
At 1st level, a magus can expend 1 point from his arcane pool as a swift action to grant any weapon he is holding a +1 enhancement bonus for 1 minute. For every four levels beyond 1st, the weapon gains another +1 enhancement bonus, to a maximum of +5 at 17th level. These bonuses can be added to the weapon, stacking with existing weapon enhancement to a maximum of +5. Multiple uses of this ability do not stack with themselves.
Fighter, advanced weapon training - Warrior Spirit (Su)
The fighter can forge a spiritual bond with a weapon that belongs to the associated weapon group, allowing him to unlock the weapon's potential. Each day, he designates one such weapon and gains a number of points of spiritual energy equal to 1 + his weapon training bonus. While wielding this weapon, he can spend 1 point of spiritual energy to grant the weapon an enhancement bonus equal to his weapon training bonus. Enhancement bonuses gained by this advanced weapon training option stack with those of the weapon, to a maximum of +5. The fighter can also imbue the weapon with any one weapon special ability with an equivalent enhancement bonus less than or equal to his maximum bonus by reducing the granted enhancement bonus by the amount of the equivalent enhancement bonus. The item must have an enhancement bonus of at least +1 (from the item itself or from warrior spirit) to gain a weapon special ability. In either case, these bonuses last for 1 minute
Arcanist, Arcane Weapon Exploit
As a standard action, the arcanist can expend 1 point from her arcane reservoir to enhance her weapon. The weapon is treated as magic for the purposes of overcoming damage reduction. At 5th level, the weapon gains a +1 enhancement bonus, which increases by 1 for every 4 levels beyond 5th (to a maximum of +4 at 17th level). These bonuses can be added to the weapon, stacking with existing weapon bonuses to a maximum of +5. An arcanist can also use this exploit to add one of the following weapon special abilities: dancing, defending, distance, flaming, flaming burst, frost, icy burst, keen, shock, shocking burst, speed, spell storing, and throwing. Adding these special abilities replaces an amount of enhancement bonus equal to the ability's cost. Duplicate special abilities do not stack. If the weapon is not magical, at least a +1 enhancement bonus must be added to it before any other weapon special abilities can be added. The benefits are decided upon when the exploit is used, and they cannot be changed unless the exploit is used again. These benefits only apply to weapons wielded by the arcanist; if another creature attempts to wield the weapon, it loses these benefits, though they resume if the arcanist regains possession of the weapon. The arcanist cannot have more than one use of this ability active at a time. This effect lasts for a number of minutes equal to the arcanist's Charisma modifier (minimum 1).
This spell functions like magic weapon, except that it gives a weapon an enhancement bonus on attack and damage rolls of +1 per four caster levels (maximum +5). This bonus does not allow a weapon to bypass damage reduction aside from magic.
So the Arcanist's arcane weapon seems to indicate that this one is more like greater magic weapon, but the others are unknown.
These are the ones that I know of, if I have missed anything which grants this type of ability, let me know and I will add it to the list.