MadMorbius

Yes I can, but it's like describing the difference between an SUV, a sports car and a pickup truck. They all share common elements but are intended for different usage.

Essentially, you have four basic categories. Plate carriers, assault vests, chest rigs, and load-bearing vests. All of them come in vastly different or remarkably similar designs.

Within those four categories, there are two design principles; modular, or fixed. Fixed systems are just that; a platform with permanently affixed pouches typically designed for a specific purpose. For example, a "Rifleman's Chest Rig" or a "Delta Operator Assault Vest".

Modular systems allow you to choose the pouch layout and greatly increases the functionality and usability of the platform by allowing you to equip for mission-specific requirements. Modular systems come in a myriad of designs, the most common being MOLLE.

All of the items you've listed are Molle-compatible armor carriers. They're designed to take hard plates, and with no plates (or replica plates) may not keep their form properly or adequately distribute load.

The RRV and MBSS are partial-coverage plate carriers. The sides are open. These rigs are typically worn overtop of soft armor carriers like the BCS carrier.

The FSBE, CIRAS and RAV are all releasable full-coverage vests that integrate soft armor and hard plates. They're all very similar in design, although comfort varies.

In a word, the difference is REAL ESTATE. How much space do you need for your loadout? Space is limited on the plate carriers. The releasable vests have a lot more room for goodies.