Here's an interesting FPS oddity: a mod created for training Canadian Federal Law Enforcement folks, now freely available for the Federal Law Enforcement training needs of you and me at home.
The project was created using the truly excellent SWAT4 (that's an Irrational game, development-history fans) and includes a number of custom weapons and playable civilians, that training types can use to make the best-laid plans of their trainees go awry. The agencies responsible have even included their contact details for training tips for other police-folk to make the most of the mod.
The training project was created with help from the 10-David SWAT gaming fan community. Good work, chaps.