[git] Adding a collaborator to my free GitHub account?

I created a GitHub account, and I want to give someone write access so he can push just like me, there is a way to add a collaborator with a free plan? If not, what can I do? (besides buying a paid account, which I'll do in the future)

Please note that Github now allows an unlimited number of collaborators even on a free account. See https://github.com/pricing.

FYI for future readers. The instructions above are outdated, in particular step 2:
2. Click on Settings button

Go to Manage Access page under settings (https://github.com/user/repo/settings/access) and add the collaborators as needed.

Screenshot:

project link:

https://github.com/your_username/you_repo_name/settings

you will get a page like this, go to Collaborator and add collaborator

In the repository, click Admin, then go to the Collaborators tab.

Yes the set of instructions above are outdated. For the new GitHub the Settings button must be clicked.

Also the person you try to add as a collaborator must have an existing GitHub account. In other words he should have signed up on GitHub first because it is not possible to send collaboration requests merely by typing in the email address of the collaborator.

It is pretty easy to add a collaborator to a free plan.

1. Navigate to the repository on Github you wish to share with your collaborator.
2. Click on the "Settings" tab on the right side of the menu at the top of the screen.
3. On the new page, click the "Collaborators" menu item on the left side of the page.
4. Start typing the new collaborator's GitHub username into the text box.
5. Select the GitHub user from the list that appears below the text box.
6. Click the "Add" button.

The added user should now be able to push to your repository on GitHub.

2020 update

It's called Manage access now.

Go to your private repo, click the Settings tab, and choose Manage access from the menu on the left. You are allowed up to three collaborators with the free plan.

Note: If the account is an individual account you can still add collaborators that can do a variety of tasks, but a collaborator can't (as far as I know) sign the app in Xcode and submit it to the app store. You need an organization account for that kind of collaborator.