Multiple GitHub accounts on the same computer?

All you need to do is configure your SSH setup with multiple SSH keypairs.

• This link is easy to follow (Thanks Eric):

  http://code.tutsplus.com/tutorials/quick-tip-how-to-work-with-github-and-multiple-accounts–net-22574

• Generating SSH keys (Win/msysgit):

  https://help.github.com/articles/generating-an-ssh-key/

Relevant steps from the first link:

1. Generate an SSH-key:

   ssh-keygen -t ed25519 -C "john@doe.example.com"
   

   Follow the prompts and decide a name, e.g. id_ed25519_example_company.

2. Copy the SSH public-key to GitHub from ~/.ssh/id_ed25519_doe_company.pub and tell ssh about the key:

   ssh-add ~/.ssh/id_ed25519_doe_company
   

3. Create a config file in ~/.ssh with the following contents:

   Host github-doe-company
     HostName github.com
     User git
     IdentityFile ~/.ssh/id_ed25519_doe_company
   

4. Add your remote:

   git remote add origin git@github-doe-company:username/repo.git
   

   or change using:

   git remote set-url origin git@github-doe-company:username/repo.git
   

Also, if you’re working with multiple repositories using different personas, you need to make sure that your individual repositories have the user settings overridden accordingly:

Setting user name, email and GitHub token – Overriding settings for individual repos
https://help.github.com/articles/setting-your-commit-email-address-in-git/

Hope this helps.

Note:
Some of you may require different emails to be used for different repositories, from git 2.13 you can set the email on a directory basis by editing the global config file found at: ~/.gitconfig using conditionals like so:

[user]
    name = Default Name
    email = defaultemail@example.com

[includeIf "gitdir:~/work/"]
    path = ~/work/.gitconfig

And then your work-specific config ~/work/.gitconfig would look like this:

[user]
    name = Pavan Kataria
    email = pavan.kataria@example.com

Thank you @alexg for informing me of this in the comments.