Open Broadcaster Software (OBS) is a free and open source software used to record and/or live stream. It has support for Twitch and YouTube live streaming with the ability to automatically connecting the account of such service directly in OBS.

OBS can be downloaded here.

Some additional programs and plugins that can be used to either improve the livestreaming engagement or give chat control of some aspect of the stream can be found there:

• lioranboard a powerful streamdeck alternative with support for Twitch's channel points.
• Streamer.bot like lioranboard but with the ability to use C# for scripting and is quite user friendly.
• Touch portal allows to use a smartphone or a tablet like a streamdeck. Has (paid?) support for Twitch channel points.
• StreamFX a plugin for OBS which adds extra filters and source mirror to OBS. (A must have for any advanced setup).
• Move Transition allow to create move filters which can be used to automatically slide things on the screen, and can be used for transitions. This can also be used for creating countdowns on OBS.