Plan 9 as a whole is a pretty good IDE for general development - excels at C, shell scripts, Go, and similar. Having been created explicitly to OS differs from older (POSIX/VMS era) OSes by making GUI, architecture portability, namespaces, user-level filesystems, software services, network transparency and distributed computing first-order concerns.
For those unable to switch outright, I wholeheartedly recommend plan9port[0] - an almost complete set of utilities and protocols from Plan 9, ported to run in Linux, MacOS X, and OpenBSD userspace. It's being actively developed[1] by the 9fans community.
plan9port comes with both sam and acme[2] programmers' text editors.
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[0] https://9fans.github.io/plan9port/