What lawn diseases are there?

Snow mold
(Microdochium nivale / pink snow mold)

Sources: Rasenprofi - CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=43906946&https://commons.wikimedia.org/w/index.php?curid=43906900

Gray snow mold
(Typhula incarnata, Tyhula rot, white/grey snow mold) 

Source:https://www.rasenprofi.de/infos/fileadmin/_processed_/csm_Wurzelhalsfaeule_grauerSchneeschimmel_8045e9edea.jpg

Red-tippedness
(Laetisaria fuciformis)

Source: By Torben von Elling - CC BY-SA 3.0 en,https://commons.wikimedia.org/w/index.php?curid=42889843

Dollar stains
(Sclerotinia homoeocarpa)

Source: By Glenobear - Own work, Public domain,https://commons.wikimedia.org/w/index.php?curid=11904740

Leaf spots
(Drechslera poae, Curvularia)

Source:https://www.rasenprofi.de/infos/fileadmin/_processed_/csm_Blattfleckenkrankheit_a902e4d3c5.jpg

Rust
(Puccinia)

Source:https://pflanzenschutzdienst.rp-giessen.de/oeffentliches-gruen/rasen/krankheiten/rost/

Root rot
(Pythium ultimum, Pythium graminicola)

Source:https://www.maag-garden.ch/de/produktsuche/nach-schaden/pythium-wurzelfaeule-rasen-507.php?highlight=wurzelf%C3%A4ule

Root burn

Source:https://www.rasenprofi.de/infos/fileadmin/_processed_/csm_Wurzelbrand3_788a13a38a.jpg

Slime molds
(Mycetozoa or Eumycetozoa)

Source:https://www.rasen-blog.com/blog/schleimpilze-im-rasen/

Blue-green algae

 Source:https://www.gartencenter-meier.ch/gartenfrage/schwarze-flecken-im-rasen-5032

Brown Patch / Yellow Patch

 Source:https://www.syngenta-turf.de/krankheiten/rhizoctonia-brown-patch-yellow-patch

Gray Leaf

Source:https://www.maag-turf.ch/news/schaderreger/gray-leaf-spot-wie-sich-die-krankheit-entwickelt

Blackleg
(Gaeumannomyces graminis, Take-all-Patch)

Source:https://www.maag-garden.ch/de/produktsuche/nach-schaden/gaeumannomyces-schwarzbeinigkeit-rasen-501.php

Summer fusariosis
(Fusarium culmorum, Fusarium poae)

Source:https://www.rasenprofi.de/infos/fileadmin/_processed_/csm_Sommerfusarium_939f34017e.jpg

Anthracnose

Source:https://www.rasenprofi.de/infos/fileadmin/_processed_/csm_Anthraknose_263e4a4d64.jpg

Witch rings

Source:https://www.rasenprofi.de/infos/fileadmin/_processed_/csm_Hexenringe_Hutpilze_7de1e9eae7.jpg

Powdery mildew

Source:https://img.gartenjournal.net/wp-content/uploads/mehltau-rasen.jpg