Pariyatti Learning Center is offering a free PDF download of a :
Comprehensive Manual of Abhidhamma by Ven. Bhikkhu Bodhi.
The Abhidhamma Pitaka (abhidhammapiṭaka) is the last of the three pitakas (Pali for "baskets") constituting the Pali Canon, the scriptures of Theravāda Buddhism. The Abhidhamma pitaka is a detailed scholastic reworking of material appearing in the Suttas, according to schematic classifications.