Short answers, pulled from the story.
ABRSM was founded in 1889 by Alexander Mackenzie, then Principal of the Royal Academy of Music, and George Grove, the founding Director of the Royal College of Music. They combined their institutions into a joint examining board to run local exams.
ABRSM conducts exams in over 90 countries each year, with more than 600,000 candidates sitting its exams annually.
ABRSM offers three diploma levels: ARSM, LRSM, and FRSM. ARSM requires a 30-minute recital; LRSM requires a 45-minute recital plus a 2,000-word essay; FRSM requires a 55-minute recital and a 3,500-word essay. All three have Grade 8 as a prerequisite for the performance pathway.
ABRSM grades sit on the UK's Regulated Qualifications Framework. Grades 1-3 are at RQF Level 1 (IGCSE D-G), grades 4-5 at Level 2 (IGCSE A*-C), and grades 6-8 at Level 3 (A Level or IB Diploma). The ARSM diploma is Level 4, LRSM is Level 6 (bachelor's degree), and FRSM is Level 7 (master's degree).
The current eight-grade structure was introduced in 1933. Originally ABRSM offered only two grades, equivalent to today's grades 6 and 7; the lower grades were added in response to demand from beginner students.
Since 2009 ABRSM has released several apps including Aural Trainer for iPhone, Speedshifter for tempo-adjusted practice, Melody Writer for music theory, and Piano Practice Partner for iOS and Android, which covers grades 1 to 3 by playing one hand while the student plays the other.