Which of iOS apps allow customizing font size?
(please contribute to the list with any other apps, and feel free to edit to make the list more accurate--this is a community wiki answer)



Notation for the list below:


With few exceptions, any app falls into on of these categories:


it supports System Settings > Dynamic Type and Bold Text (I mark it as "Dynamic&amp;Bold" below)
OR also supports System Settings > Larger Text (I mark as "Larger Text")
OR has its own app-specific font size settings ("App settings")
OR has NO font size customization whatsoever ("No customization")

For each app, I also specify how its maximum text size compares to standard system apps at maximum Dynamic Type setting if different (the app font is Smaller or Larger than in system apps)--to make it easier for a given app to understand its text size limit, given only few minutes with built-in apps only at Apple outlet.




Social networks

Facebook: 
 - all UGC (News Feed, User Timeline, Individual post and comments): Dynamic&amp;Bold (since 2015-Nov-06); much Smaller 
 - app interfaces: No customization; smaller

Twitter: 
 - timeline: App settings (3 sizes); smaller 
 - settings screen: Dynamic&amp;Bold

Google+: No customization; Much smaller

Instagram: No customization; Much smaller

VKontakte (both iPad- and iPhone apps): No customization; Smaller



Email apps

Mail: 
 - plaintext emails: Dynamic&amp;Bold 
 - HTML emails: font scales only with Larger Text, but not with Dynamic Type(!); but can be much smaller than for plain text emails / than in other apps

GMail:  No customization; Smaller (both for plaintext and HTML emails)

Google Inbox:  No customization; Smaller (both for plaintext and HTML emails)

AirMail: Dynamic Text, App Settings; no LargerText support (text gets smaller instead)

Calendar (by Apple): Dynamic&amp;Bold



Task managers

OmniFocus:
- Dynamic&amp;Bold throughout the app
- LargerText for leaf-level outline items and Note editing only; No for outline groups

Things: No customization; smaller



Instant Messengers

Messages (iMessage):
- history of chat with a contact: LargerText
- list of contacts on left sidebar: Dynamic&amp;Bold

Skype: No customization; Much Smaller

Telegram:
- history of chat with a contact: Dynamic Type (no Bold Text); smaller
- list of chats: No customization; Smaller



Web browsers

Safari:
- regular browsing: No customizaion; pinch to zoom leads to horizontal scrolling. Smaller.
- has a special Reader Mode with App Settings: wide range of sizes, comparable to the range of Larger Text. Works only for article-type web pages, not everywhere.

All other browsers tried (Google Chrome, Opera, Yandex Browser, iCabMobile): No Customization; pinch to zoom leads to horizontal scrolling. Smaller.



Office documents

Google Drive: No Customization

Google Docs: No customization: only document zoom, leads to horizontal scrolling. Smaller

Google Sheets: No Customization: only document zoom, leads to horizontal scrolling. Smaller



Maps

Google Maps: No customization; Smaller

Apple Maps: Dynamic Type only



Other built-in apps

Settings: Dynamic&amp;Bold

Notes: LargerText

Reminders: LargerText

home screen: No customization

built-in keyboard: Bold Text only



Other third-party apps

Pocket:
- list of articles: Dynamic&amp;Bold
- aricle body: App settings: wide range of sizes, comparable to the range of Larger Text

Google Keep: No Customization. Much Smaller.