The icons are mostly from openclipart.org and iconarchive, flaticon.com IIRC.

Going to search them anew (proves somewhat difficult), to add proper source references here...

back.png	openclipart / redrawn
clear.png	combined / custom
clipboard.png	http://www.iconarchive.com/show/buuf-icons-by-mattahan/Clipboard-Manager-icon.html
computer.png	https://openclipart.org/detail/5012/laptop
copy.png	???
csv.png	http://www.iconarchive.com/show/windows-8-icons-by-icons8/Files-Csv-icon.html
ethernet.png	https://openclipart.org/detail/174481/network-interface-card-labelled
html.png	http://icongal.com/gallery/icon/2645/128/html_natsu
icon.beta.png	http://www.istockphoto.com/de/vektor/beta-testing-orange-runde-grunge-stempel-auf-weiss-gm489727300-74813301?irgwc=1&esource=AFF_IS_IR_SP_FindIcons.com_339640&asid=FindIcons.com&cid=IS
icon.cloud.png	https://openclipart.org/detail/179894/stylized-basic-cloud
icon.cmd.png	app icon
icon.controller.png	https://openclipart.org/detail/181334/microcontroller
icon.copy.png	https://openclipart.org/detail/199334/primary-copy
icon.date.png	-
icon.events.png	-
icon.exchange.png	https://openclipart.org/detail/5332/envelope-1
icon.extras.png	https://openclipart.org/detail/167937/present-ns
icon.finduser.png	user icon + https://openclipart.org/detail/31033/architetto-lens-lente
icon.fire.png	https://openclipart.org/detail/876/fire-june-holidays
icon.firewall.png	https://openclipart.org/detail/171429/firewall
icon.folder.png	https://openclipart.org/detail/38923/open
icon.godzilla.png	https://openclipart.org/detail/170216/godzilla-danger
icon.info.png	https://openclipart.org/detail/33733/info-sign
icon.install.png	-
icon.key.png	https://openclipart.org/detail/3330/key
icon.license.png	-
icon.lnk.png	-
icon.log.png	-
icon.mfcmapi.png	app icon
icon.network.png	https://openclipart.org/detail/217136/network-card-from-behind
icon.notes.png	https://openclipart.org/detail/183333/sticky-cube-notes
icon.office.png	https://openclipart.org/detail/216806/office-building
icon.powershell.png	app icon
icon.printer.png	https://openclipart.org/detail/171015/laser-printer
icon.registry.png	-
icon.samba.png	https://openclipart.org/detail/200906/primary-sambaserver
icon.server.png	https://openclipart.org/detail/175114/tools-server
icon.tools.png	-
icon.unlock.png	-
icon.users.png	https://openclipart.org/detail/35347/tango-system-users
icon.wmi.png	https://www.techspot.com/downloads/6603-tweakingcom-repair-wmi.html
ping.png	https://openclipart.org/detail/174481/network-interface-card-labelled
sweep.png	https://openclipart.org/detail/182731/sweep
to-user.png	https://openclipart.org/detail/5572/computer-user
user.png	https://openclipart.org/detail/4749/male-user-icon
splash.jpeg	https://www.publicdomainpictures.net/en/view-image.php?image=239644&picture=abstract-background