Short answers, pulled from the story.
The Frankfurt proposals, also called the Frankfurt memorandum, were peace terms the Allies offered French Emperor Napoleon I in November 1813 during the War of the Sixth Coalition. Drafted at Frankfurt under Austrian foreign minister Klemens von Metternich, they would have let Napoleon remain emperor while reducing France to its so-called natural borders.
Austrian foreign minister Klemens von Metternich directed the drafting of the Frankfurt proposals. The Allies, meeting at Frankfurt, prepared the terms under his close supervision, and British diplomat Lord Aberdeen was present and accepted the moderate terms.
Napoleon delayed his response because he expected to win the war outright, and by the time he tried to accept the terms it was too late. Austria had already signed treaties with the Allies by December, and London had rejected the terms over fears that Belgium could become a base for invading Britain, so the offer was withdrawn.
Under the proposals, France would have kept Belgium, Savoy, and the Rhineland, territory annexed during the early wars of the French Revolution. France's natural borders would have been the Pyrenees against Spain, the Alps against Italy, and the Rhine against the German states, while it gave up parts of Spain, Poland, and the Netherlands, plus most of Italy and Germany east of the Rhine.
Napoleon was forced to abdicate on the 6th of April 1814, after military defeats in France and the surrender of Paris. This came after he refused the Allies' harsher replacement terms, which demanded France retreat to its 1791 boundaries and lose Belgium and the Rhineland.
Napoleon suffered a decisive defeat at the Battle of Leipzig, after which the Allies recaptured most of Germany up to the Rhine. Metternich then took the initiative to offer Napoleon peace terms in November 1813, aiming for a peaceful end to the War of the Sixth Coalition.