Kappa UI

Kappa UI is a tool for displaying an interactive Twitch chat overlay over any game, intended for streamers without dual monitors.

It currently supports two modes. "Overlay window" is the preferred mode, it creates a popup window that displays the overlay. It does not interfere with games and is thus the most stable. However, it might cause performance issues on certain computers (due to transparency being handled by Windows) and will not work with fullscreen (not borderless window) games.
The other mode is DirectX hooking similar to Fraps & co. It lacks the stability and might not support all games very well, and is only recommended if the Overlay window doesn't work. Currently it supports DX9/10/11 games, both 32 and 64-bit. An important difference is that this mode will cause Fraps and broadcasting software to capture the overlay as well (actually, not always - in DX10/11 it depends on the order the hooks were installed in). It can also interfere with Fraps - if the overlay isn't shown, try turning Fraps off and trying again (it can also crash the game if you use both).