Is Bitcoin completely Open-Source? I am newbie in this area.

As I understand, Bitcoin was started as open-source project; But what about now?

I see on Github there is 'Bitcoin Core', is it bitcoin repository?
https://github.com/bitcoin/bitcoin

Or maybe government or corporations already bought it, like, for example, Github..
Bitcoin Core is open source under an MIT license, and is the original software implementation of a Bitcoin full node, though there are others. Most nodes run Bitcoin Core, but don't have to. Bitcoin could be defined as a network of users that agree to the same consensus rules, which means they don't all have to run the same exact software.

The MIT License (MIT)

Copyright (c) 2009-2018 The Bitcoin Core developers
Copyright (c) 2009-2018 Bitcoin Developers

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.


See COPYING