When you talk about open source, first thing that comes to mind is probably Github. It is an awesome "social network" for developers and hosts lots of projects. Also it makes working on team or open source projects a lot easier and have awesome integrations (Travis, Coveralls and so on). Github also provides service for open source for free and it is a rare case nowadays that a free service doesn't make you it's product.
But Github also a closed source by itself and making open source projects to depend on closed source platform isn't a good idea and never was. Free software supporters used it anyway as it was independent and had user's trust.
Github was losing money and needed to find a way to increase it's profit. After all, it is a for-profit company and it's investors needs money. Giving too much power to such platforms always ends badly as needs for profit puts community needs behind. More on that is stated in this article: Wired article
Another alternate to Github is Bitbucket, owned by Atlassian. It provides free private repositories with limited number of members for personal use. It is more like cheaper version of Github for enterprise use and has better integration with Atlassian products like Jira.
Gogs, Gitea, Gitlab CE and other self-hosted solutions - For private usage, you can just use git itself without fancy UI. These solutions are good for projects developed by multiple groups and community. However, to make contribution to your project others will need to register on your system, configure their profiles and get used to you UI and issue management. It is much better than using maillists or FTP but not great. The main point behind Github is the social part. You use it for your personal projects, for work related projects and at the same time you can contribute to other projects using the same network. That attracts a lot of people to the project and that is the main reason for many free and open source projects to choose Github, Bitbucket or Gitlab.
Gitlab uses open source business model and offers Community Edition (MIT License) which you can host by yourself and has most of the key features of Gitlab. So even if it makes mistakes in future, community can easily fork it and continue development - making it future-proof. It is also a social coding platform like Github and more projects are starting to use it. It also offers unlimited private repositories both for personal and for enterprise use, it has own Continuous Integration & Deployment (CI) free to use. Another great news, they are going to implement federated merge requests (pull requests) such that, you can use both private hosted version and centrialized ones and send merge requests (Github's Pull Requests) to projects using both versions - Gnome uses gitlab.gnome.org and this feature will allow you to make contribution to Gnome projects directly from Gitlab.com or other networks using Gitlab. You can check some awesome features at this page.
As you already know, Microsoft bought (agreed?) to buy Github for $7.5 billion. Well, that is good for Github as they will pay their investors and they will have resources for the future. Also Microsoft makes a lot of contributions to open source projects since Satya Nadella became CEO and they are supporting free software events. More contributors, more free and open source projects are better for the community and we like it. But recovering trust takes more time specially for a company that was so evil agains open source in the past, it's Embrace, extend, and extinguish and even has problems nowadays: No, Microsoft does not love open source. May be one day they will gain trust but it is too soon.
Will Microsoft improve Github and leave it independent after spending so much money and more later (Github's infrastructure requires a lot of money and paid users do not cover it yet) or will it end like Skype, Nokia and many other projects? Maybe more limitations for free users, requiring MS Live account, exclusive functionalities for their Azure platform and their Visual Studio Code and so on. We will see later, but that is not point and it shouldn't be reason to leave the platform. Microsoft buying Github reminds us base problem with Github - being closed source, for-profit and hosting most of the major free and open source projects. That gives huge powers to Microsoft over free software projects and it is completely wrong - They can use it to eliminate alternates by providing locking features that only can be used in Github, which is stated well in "Embrace, extend, and extinguish" article. A major corporation like Microsoft, Google, Facebook or Apple should not have such power. Using Github for such projects already was a mistake and continuing to use is worse.
For that reason I already started to move our Free Software Community in university to Gitlab (community exposes a sample behaviour for new members) and other open source projects that I'm maintaining. Also moved private repositories from Github and Bitbucket to avoid usage of multiple networks. Of course it is not the end for Github and most will continue to use it for some other projects (just like #DeleteFacebook, it is a social network and won't die unless most of it's users related to you leaves to the same platform as you) if Microsoft will not ruin it. Gitlab seems the safest "social" solution for now.
Additional reading: Ok, now there is quite big movement from GitHub to GitLabShare on Twitter Share on Facebook