People who have helped GNU Parallel different ways.

Wu Zhenyu: Code snips for --completion zsh.
Morten Rønne: Donating his old Mac for testing.
Renan Valieris: Maintaining GNU Parallel for Anaconda Cloud.
Jakub Kulík: Maintaining GNU Parallel for Solaris-userland.
Rich Burridge: Maintaining GNU Parallel for Solaris-userland.
Jonathan Kamens: Bug patch for chomp.
John Rusnak: Feedback on all documentation.
FrithMartin: Bug patch for orphan blocks.
Rasmus Villemoes: Code snips for signal processing.
Martin d'Anjou: Code snips for signal processing.
rici@stackoverflow.com: Documentation on exporting arrays using --env.
Malcolm Cook: The idea to use a general perl expression as replacement strings.
Ævar Arnfjörð Bjarmason: Reading the whole code.
Christian Netrwal: CPU detection code for AIX.
alpinelinux.org/users/ncopa: Maintaining GNU Parallel for Alpine GNU/Linux.
Ondřej Surý: Maintaining GNU Parallel for Debian GNU/Linux.
Rogério Brito: Maintaining GNU Parallel for Ubuntu GNU/Linux.
Tim Harder: Maintaining GNU Parallel for Gentoo GNU/Linux.
Chris Howey: Maintaining GNU Parallel for FreeBSD.
cheusov: Maintaining GNU Parallel for NetBSD.
https://fedoraproject.org/wiki/User:Golfu: Maintaining GNU Parallel for Fedora GNU/Linux.
Pascal Stumpf: Maintaining GNU Parallel for OpenBSD.
Sandro Cazzaniga: Maintaining GNU Parallel for Mandriva/Mageia.
Alan Coopersmith: Maintaining GNU Parallel for Solaris.
jengelh@inai.de: Maintaining GNU Parallel for openSUSE.
Timothy Redaelli: Maintaining GNU Parallel for Arch GNU/Linux.
Michael Shigorin: Maintaining GNU Parallel for Alt GNU/Linux.
Jesse Alama: Maintaining GNU Parallel for Fink.
jacknagel: Maintaining GNU Parallel for Homebrew.
Jonathan Palardy: Maintaining GNU Parallel for Homebrew.
Tim Cuthbertson: Maintaining GNU Parallel for 0install.
Michael Perzl: Maintaining GNU Parallel for AIX.
Peter Simons: Maintaining GNU Parallel for Arch GNU/Linux.
Fethican Coşkuner: Maintaining GNU Parallel for Pardus.
Wayne E. Seguin: CPU detection improvement for Mac OSX.
Michał Markowski: OpenBSD CPU detection.
Drew Frank: Work on --results.
Javier Tarradas: HPUX CPU/core detection.
Anders F Björklund: niceload: Darwin version of --io --mem --swap.