Oh man I have a bunch of these. mainly geared toward a heavy mohawk game.
1. Restricted Gear Quality - Some characters have backgrounds that require things that don't jive with RAW limits. To suit this I have removed the RG quality from the game. Characters may take as much restricted gear as they can afford, however each piece lands them a distinctive style quality with no BP bonus. The Availability 20 cap is still enforced.
2. Over Modding Gear - Over modding is also allowed up to double the normal capacity of the object. Each object that is over modded is also subject to the Distinctive Style penalty. This stacks with the Restricted Gear rule, so an Availability 16F assault rifle that is over modded receives a level 2 Distinctive Style penalty.
3. Gyro Rigs (Two Gun Mod) - A gyro rig may be modified to have a second arm on it (double the cost and availability). This can be taken a character creation or built using a Logic + Armorer (8, 1 Hour) Extended Test. This allows two weapons to be mounted on the same rig. These weapons split the recoil compensation regardless of weapon type.
4. Gyro Rigs (One Hander) - Since the arm of the rig attaches under the barrel it is considered to be a suitable replacement for a second hand. This means that weapons requiring two hands (assault rifles, machine guns) may be fired one handed, if mounted in the rig, with no penalty. This can be combined with the Two Gun Mod up top for crazy gun bunny hijinks.
5. Twin-Link Program - Twin-Link is a software mod for smartlinks allows users to link their smartguns together and fire them in tandem. This program even allows two weapons, that normally take a complex action to fire, to be used together in the same action phase. When firing, make one roll, add the base DV/AP of both weapons plus net hits. Any other DV mods (Ammo, Full burst, high velocity) apply only once. If mixing guns, both must be set to the same firing mode and the lower weapon range is used, as well as the lower DV/AP if ammo is mixed. Both guns must be smartguns and a smartlink is required. Turning on or off Twin-Link is a free action. Availability 20F, 12,000 Nuyen
A few more, but I'll put 'em up later...