Project Sicario is an ongoing community-run open-source project to improve and automate gameplay mods in Project Wingman.
Project Sicario consists of two major components: Project Sicario Merger (PSM) and the Project Sicario Builder (web app also just referred to as Project Sicario). The two parts share a common patching engine underneath, but work quite differently and serve similar but not identical purposes.
Project Sicario at a high level is a semi-automated tool for merging otherwise incompatible gameplay changes by building them all into a single merged mod the game can load. It does this by relying on Sicario "patches": rather than being modified game files, patches are essentially instructions of what to change in the game files that Sicario then applies to create a mod.
This document is only a brief summary of the major components. There's a ton of information on how Project Sicario works in the Sicario Builder docs and the PSM mod page.
There's a heap of detail on actually installing, using and managing PSM on the mod page.
Project Sicario Merger (PSM) is the newer component of the pair and is installed and run locally on your PC. PSM loads any compatible patches it can find in your game directory: Sicario presets, PSM-compatible mods and other Sicario-built mods, compiles them all together and applies them to the base game files to build a single merged mod file with all the changes applied that the game can then load.
There's also quite a bit of detail on Project Sicario Builder available in the app at sicario.modding.app
The Project Sicario web app (now referred to as Builder for clarity) is the earlier part of the Sicario project and is based on the same basic design as PSM but without needing to install anything at the cost of reduced functionality.
The Project Sicario Builder can also build a ready-to-run merged mod from multiple changes, but only from the patches uploaded to the app, not from other mods. It becomes much more powerful when combined with PSM since you can use the Builder to create your own personalised preset with any combination of the mods available in the app, then use it with PSM (see below).
When you choose and customise your build from the patches available on Project Sicario Builder, you have the option to save all of your selections and customisations as a Sicario preset. If you are also using PSM you can save this file to your mods folder, then PSM can load this preset and include it with any other PSM-compatible mods.
This means you can create a customised preset with the exact combination of changes and tweaks available from the Builder, but still use PSM-compatible skins, or load patches embedded in other mods you have installed, that might not be available on the Builder.