This Sublime Text plugin allows you to compare, merge and manipulate lists of things,
whether they are todo items, lists of files or arrays from API responses:

Switch to a file with a list you want to modify and select an operation to perform from the Command Palette
(or using Edit -> Lines - Multisets menu).
The result is all items from both lists. Example:
| List 1 | List 2 |
|---|---|
| one | two |
| three | three |
| four | four |
| four |
Result: one, two, three, three, four, four, four
The result is items from both lists, but only one item for every match. Example:
| List 1 | List 2 | Match |
|---|---|---|
| one | two | |
| three | three | ✔️ |
| four | four | ✔️ |
| four |
Result: one, two, three, four, four
The result is only items that exist in both lists. Example:
| List 1 | List 2 | Match | Result |
|---|---|---|---|
| one | two | ||
| three | three | ✔️ | three |
| four | four | ✔️ | four |
| four | five | ||
| five | five | ✔️ | five |
| five | five | ✔️ | five |
The result is items from list 1 that don't have a match in list 2. Example:
| List 1 | List 2 | Match | Result |
|---|---|---|---|
| one | two | one | |
| three | three | ✔️ | |
| four | four | ✔️ | |
| four | five | four | |
| five | five | ✔️ | |
| five | five | ✔️ |
The result is items that exist in only one of the lists. Example:
| List 1 | List 2 | Match |
|---|---|---|
| one | two | |
| three | three | ✔️ |
| four | four | ✔️ |
| four | five | |
| five | five | ✔️ |
| five | five | ✔️ |
Result: one, two, four, five