Sometimes billed as a plot "machine", Plotto is a system of cataloged story components that may be combined to suggest plots of varying degrees of detail and complexity for writers. It functions like a series of story blocks that may be combined, swapped and rearranged into countless combinations of stories. Published as a book with a strange and complex system of indexing this app simplifies the process of creating plots and removes most of the strange algebra-like coding system.
Plotto was created by William Wallace Cook (born in Marshall, MI in 1867) who was a wildly prolific writer with hundreds of works of fiction to his name--many of which were adapted into films. In 1910 he produced more than 1 book a week and was nicknamed "the man who deforested Canada" for the volume of stories he fed into the old pulp-magazine mill. He spent five years composing Plotto before finally publishing it in 1928. A young Alfred Hitchcock and Earle Stanley Gardner (author of the Perry Mason books) were early adopters of the work.
Analyzing every story he knew with an OCD-level obsession and breaking them down into their components, Cook cataloged well over 3,000 clauses, subclauses, clause fragments and optional developments. The total number of unique plots Plotto can produce is truly staggering.
Select the A, B and C clauses to create the "Master Plot." Although any combination of clauses may be considered valid, it is clear from the original charts that there was a loose association between the A clauses and the B clauses. To try to preserve that, the associated A clause is listed in parenthesis at the end of each B clause. You can use that as a guide or ignore it as you like.
If you are truly stuck for ideas, you can set one or more clauses to "Pick Random Item" and have the app pick the masterplot for you.
When all three clauses are selected the entire plot will display in the lookup window along with the ID of one or more suggested clauses to further expand the plot. You can then append or prepend this information to the notes window at the bottom of the page by clicking on the respective buttons below or you may manually edit this information as you wish.
Each clause may include a number of suggested prequel and sequel clauses as well as related clauses in parentheses within the text. Often clauses are divided into parts and sometimes may contain optional choices which will be indicated by brackets (i.e.  for option 1) You may look up these clauses by typing in the ID of the clause (a number and sometimes a single letter) in the text field below the lookup window and click on the "Get Clause" button. The identified clause will appear in the lookup window above. If the word "undefined" appears it means the app didn't recognize the ID of the clause entered so try again.
The clauses listed in parenthesis may sometimes include special instructions such as "change FMC to MMC" this means that, when you get the results of the clause, consider changing the Female Main Character to the Male Main Character in the description in order to be consistent with the clause that had suggested it. (Sometimes he uses the word "transpose" to switch two characters.)
If you need additional clauses beyond those suggested, you can also look them up by category. Select the "Browse by Category" drop-down list and the ID's of all clauses within that thematic category will appear in the text field to the right. Simply enter one into the Get Clause field to look up its details.
On a final note: I made as few changes to the original text as I could. Be aware that the language he used may seem rather strange to us today, and the meaning of some of the words may have shifted. Also, the editing of the original text was not perfect and his strange notations weren't always consistent. To make matters more complicated, the scan of the original text was not perfect. I did clean up as many errors as I caught. Hopefully, I did not introduce more. If/when you find one, feel free to contact me with the details and I'll try and update the lists.
Remember, all of these clauses are only suggestions meant to spark new ideas. Your creativity is still required.
A (Protagonist) Clause
B (Action) Clause
C (Terminal/End) Clause