Now, the rules here are incomplete and bare-bones, but it has the basic idea I am shooting for. It has been something I've worked on-and-off with for a long time. Eventually, I would like to submit it on the Basic Fantasy forums, like I have with my "Simple Halloween" and "Powder & Shot" supplements.
Note: I didn't include a list of proficiencies as I haven't written them yet, but it shouldn't be to hard to create your own or to search online for a list of old AD&D proficiencies.
SIMPLY PROFICIENT(version 0)
Proficiencies represents knowledge pertaining to something outside of combat and the adventuring life (well, mostly). They cover things not normally encountered or needed while exploring dungeons and catacombs, like a knowledge of history, cooking, blacksmithing, etc.
Characters start with 4 proficiencies. One represents their background, one is tied to their race, another from their character class, and another proficiency of their choice. All proficiency's start at the Basic rating.
Intelligence and Proficiencies
A high or low Intelligence score will modify a character's starting proficiencies. A character will always have at least one proficiency.
Characters gain one additional proficiency at 3rd level and every third level thereafter. They can either increase a proficiency they already possess by one step, or obtain a new proficiency at the Basic rating.
The Proficiency Check
The Proficiency Check requires you to roll equal to or under the proficiency's Proficiency Score on a d20.
A proficiency's score is: 8 + ability modifier + Proficiency Rating.
The Proficiency Rating is a measure of a character's level of knowledge of the proficiency. Each rating provides a bonus to determine the Proficiency Score. There are four different ratings; Non-proficiency (+0), Basic proficiency (+2), Expert proficiency (+4), and Master proficiency (+6).
Automatic Success and Failure
When making a Proficiency Check, a natural roll of 1 is an automatic success, while a natural 20 is an automatic failure.
The basic proficiency check assumes a static target number (TN), with nothing beyond the character's proficiency rating and natural abilities to determine their chance of success. If you wish for more variation, you can apply a modifier to target number. Beneficial circumstances would increase the TN, while detrimental conditions would lower the TN. The modifiers should range from +/- 1 to 3.
Magic Items & ProficienciesMagic items can be made to interact with the proficiency rules. Most magic items will grant the character a +1 to +3 bonus on their proficiency checks with one proficiency, or rarely, two proficiencies. Some more uncommon items might boost a character's proficiency rating, so long as they have the proficiency to begin with. Some rare magic items might even grant a character a proficiency rating even if they do not possess the proficiency. There might also be cursed items that have the opposite effect of those noted above.