kitty - A terminal emulator

Major features:

Uses OpenGL+FreeType for rendering
Supports tiling multiple terminal windows side by side in different layouts without needing to use an extra program like tmux
Supports all modern terminal features: unicode, true-color, mouse protocol, focus tracking, bracketed paste and so on.
Easily hackable (UI layer written in python, inner loops in C for speed). Less than ten thousand lines of code.
Rendering of text is done in an actual character grid, so the common problems with most Terminals when using wide characters/complex scripts do not occur. The downside is that scripts with complex glyph layout, such as Arabic do not render well.

Resources on terminal behavior