Skill Lists

Here are some lists of skills that I've found that nicely fall into groups of sevens:

THE LIBERAL ARTS

Logic

Grammar

Rhetoric

Arithmetic

Geometry (Geography)

Music

Astronomy (Calendar)

THE MECHANICAL ARTS
Vestiaria (tailoring, weaving)
Agricultura (agriculture)
Architectura (architecture, masonry)
Militia and venatoria (warfare and hunting, "martial arts")
Mercatura (trade, commerce)
Coquinaria (cooking)
Metallaria (blacksmithing, metallurgy)
The above list is per Johannes Scotus Eriugena.

Another list replaces Commerce with Navigation, Agriculture with Medicine, and Cooking with Theatrical Arts (Hugh of St Victor). Yet another list replaces Architectura with "Armaments," which broadly includes working with stones, woods, metals, sands, and clays. "The later medieval tradition arrayed the mechanical arts in a range from technological to economic subjects: shoemaking, armaments, commerce, tailoring, metalwork, and alchemy, and occasionally agriculture, navigation, and music, among others."

A bit more:
Hugh's classification strikes a modern eye in that the mechanical arts appear at the top level. Suddenly, after having no place in philosophy whatsoever, they become one of four primary divisions. As I mentioned, John the Scot claims that there are seven mechanical arts, to balance the seven liberal arts, and Hugh chooses them to parallel the trivium and quadrivium:. personifying nature, he says, “three pertain to external cover for nature, by which she protects herself from harm” (fabric-making, armament, and commerce) and “four to internal, by which she feeds and nourishes herself” (agriculture, hunting, medicine, and theatrics).[18] Hugh explains that the trivium is external and the quadrivium is internal in nature, and he thereby partially justifies his inclusion of the mechanical arts in what had previously been closed to them. In order to fulfill his claim that “These four [divisions] contain all knowledge,”[19] his classifications encompass more than is immediately suggested by their titles. For example, through some circuitous reasoning, Hugh classifies “all such materials as stones, woods, metals, sands, and clays” under “armament.”[20] He thereby includes here all technologies such as carpentry, masonry, cooperage, joinery, and metal casting.
http://www.compilerpress.atfreeweb.com/Anno%20Walton%20An%20Introduction%20to%20the%20Mechanical%20Arts%20in%20the%20Middle%20Ages%20AVISTA%202003.htm

We may find a similar list of seven mechanical arts
according to the utility of their ends in the writings of Radulphus de Campo Longo, called
the Fiery (Ardens). Radulphus mentions the following: ars victuaria—the art of feeding
people; ars lanificaria—the art of dressing people; ars architectura—the art of providing
shelter; ars suffragatoria—the art of means of transport; ars medicinaria—the art of healing;
ars negotiatoria—the skill of trading goods; ars militaria—the art of defence against an
enemy.
http://74.125.95.132/search?q=cache:zmAHQIExhGYJ:ptta.pl/pef/haslaen/a/artes.pdf+Artes+Mechanicae&hl=en&ct=clnk&cd=24&gl=us&client=firefox-a

THE MARTIAL ARTS (KNIGHT'S ARTS)

Riding

Tilting

Fencing

Wrestling

Running

Leaping

Spear-Throwing

THE FACULTY

Philosophy/Theology

History

Law

Medicine

Nature

Alchemy (often considered a mechanical art)

Arcana (added for "game balance"

Artes Magicae (the forbidden arts)
Nigromancy (demonology, necromancy, "high magic" as from a grimoire)
Geomancy (earth)
Hydromancy (water)
Aeromancy (air)
Pyromancy (fire)
Chiromancy (Divination from palms)
Scapulimancy (Divination from animal bones)

Whether they could form the foundation for a skill system is debatable, but it does have some pseudo-historical flavor!