Gaming with a physical disability, otherwise known as Accessible Gaming, presents an obvious challenge to the gamer who has the use of just one-hand. Thankfully there are several resources available to really improve the gamers experience and I will talk about some I use here, and provide links to others resources online. This page is focused on PC gaming only.
My setup is Voice control software, a Logitech G700s Rechargeable Gaming Mouse, Logitech G105 Gaming Keyboard and footpad also a mini 6-key keyboard 
My choice of games includes Diablo 3, FPS like Borderlands2, Planetside2 and RPG like Torchlight2. These all require a lot of input commands to be effective, so a mouse with lots of easy-to-use buttons is the most important part of my setup.
The foot pedals enable me to map the strafe and jump keys to foot commands, so I can circle-strafe like a ‘normal’ gamer.
First-Person Shooters (FPS) I tend to map the move forward key to a thumb mouse button, mouse-movement as freelook. Using the traditional FPS movement controls WASD are pointless if you have one-hand as you cannot target or look around you when moving.
Software
VoiceAttack is an awesome Voice Control app that greatly assists my one-handed gaming experience. I’ve created a few videos on YouTube that show the process of creating profiles & using the VoiceAttack software:
https://www.youtube.com/watch?v=MiPTJTLP5Hg
Along with the software that comes with the hardware I also use Glovepie when I have config issues with the game not recognizing my custom settings. Glovepie allows you to record any Input and map it to something else, so I could have a macro that switches to my favorite weapon and reloads it, just by pressing F12.
For challenging games with lots of commands such as Skyrim, I also use Voice commands to switch and use spells, access inventory, drink a healing potion etc.
Foot-pedals
Features: Assign any key to these foot pedals. Great for tasks like editing in Photoshop or any time you need to hold a key and click at the same time. My Pedals get equal use in Gaming and ‘serious’ tasks such as my 3D animation. A common task such as scaling an object equally across all 3 axes requires me to press the Scale icon , hold Shift and click and drag one of the X,Y or Z axes. A simple task for someone with two hands, a bloody tricky task for one-armed bandits like me. By mapping Shift to one of my foot pedals, I can press with my foot and do the rest with the mouse. This is considerably quicker than using Sticky Keys.
Other disabled gaming resources
Razer Hydra Controller
playing Rage one handed with the Razer Hydra
The GlovePIE Programmable Input Emulator (previously known as PIE) emulates input devices by using other input devices.
This means you can use the joystick in a keyboard only game (eg. DOOM3) or the keyboard in a joystick only game (eg. Return Of The King Co-op mode). Or you can control any game with a virtual reality glove, Wii Remote, Kinect, etc. Or you can create macros to do complex moves at the touch of a button (eg. Mortal Kombat). Or you can play musical instruments from your PC.
VAC – Voice Activated Commands
StickyKeys
Activate by pressing Shift five times, or:PC – Sticky Keys is found under ‘Ease of Access Center’, ‘Make the keyboard easier to use’ then ‘Setup Sticky keys’
Mac – Universal Access
Father & son build custom Minecraft controller for one-handed use
Steam controller modified for use in Skyrim
Reddit thread “Games needed for person with very little physical ability”
Reddit sub “Disabled gamers”
Online Resources
The Able Gamers Foundation