Ion
An early tiling window manager built on static frames and tabs, remembered mostly for its licence.
Tuomo Valkonen released Ion in 2000. The screen is split into frames that keep their size, and new windows land as tabs in whichever frame has focus — the opposite of most later tilers, which recompute the whole layout every time a window appears. Everything is keyboard-driven, and from Ion2 onward configuration and extensions are written in Lua.
Ion3 shipped under the LGPL plus a clause requiring distributions that carried an outdated version to rename it. Debian and others read that as an attempt to dictate packaging and dropped the program. In 2010 the code was forked as Notion, which is still maintained. Ion itself became a case study in how a single licence clause can sink an otherwise well-liked project.