
Transparent Chat Overlay
Github (free)
"An application for Windows that will display Twitch chat on top of a windowed or borderless windowed game."
It's great for single monitor users, but I still use it even though I have 2. It's great for games where you don't want o have to look away from the game for too long.
You may need to get Borderless Gaming (mentioned below) for it to show.

Chatty
Github (free)
"Chatty is a chat software specifically made for Twitch, in the spirit of a classic IRC Client. It runs on Windows and any other OS that supports Java 8 or later."
I usually keep it running in the background, when I'm streaming, so that I have my chat logs saved.
It has full twitch moderation function, which makes it incredibly handy to have on a second screen. You can use to to show users in chat, people joining/leaving chat, as well as some other handy info.

Deckboard
Mobile app (free & paid)
"Deckboard helps you create macros for Windows PC and launch them on your phone."
This is a great alternative to one of those swanky streamdecks. It connects to Twitch, OBS and Slobs, as well as Spotify and some other stuff. Makes scene changes, chat commands etc sooo much easier. The free version is just fine, but I love it so much that I dropped the few dollars for the "Pro" version. I can't imagine NOT using it now.

Lootlink.me
Free giveaways
If you're at all interested in either running giveaways, or winning stuff, this is THE website to use. It's a great tool to help your channel grow, and a fun way to try your hand at winning games to play too.
This site the only place that I'll run game giveaways on now (buh-bye Gleam.) The system they have means that giveaways are super easy to create and, once created, are hands off. No micro management needed to select the winner!
There's no sketchy advertising, or questionable permissions, so you wont be getting emails about "enhancement" products because they've sold your info.

Borderless
Gaming
Github (free)
"Borderless Gaming is a simple tool that will allow you to turn your windowed video games into "fullscreen" applications without all of the negative side effects."
Sometimes fullscreen games won't capture properly for streaming. Occassionally games are silly and won't let you tab out without minimising the game. This application helps a bunch. Basically start your game in windowed mode, then use this to fake full screen. It makes streaming games like No Man's Sky, and Spore, a lot easier. Also.. this is needed for using the Transparent Chat overlay (mentioned above.)

QuestMode
free twitch subs and donations
"Quest Mode is a platform that gives you the opportunity to participate in microsponsorships without you needing to go looking for them."
This site allows your community to earn points to subscribe to your channel, by playing mobile games or completing other goals. A lot of them are free to play, and even have donations for the streamer attached! There are some regional restrictions on offers, and sometimes the pickings can be slim, so it pays to check often.
In the past, I've had things like a free month of Shudder/Hulu, or free samples of nootropic gum. DO make sure you check the terms before you sign up for anything though.

