Here is a non-exhaustive (non-binding) list of services and applications compliant with the FIDO U2F standard.
Boxcryptor
Dropbox
Files.com
Google Drive
Amazon Web Services
Google Cloud Platform
G Suite for Education
Hangouts
SalesForce
Follow Link
Blogger
Shopify
Silverstripe
WordPress (2FA plugin)
YouTube
Binance
Bitfinex
Brave
Coinbase
DSX
Bitbucket
Github
GitLab
Jira (2FA for JIRA)
Sentry
1Password
Bitwarden
Dashlane
AuthStack
Avatar
Axiad
Centrify
Daon
DUO
ForgeRock
Gluu
Green Rocket
HelloID
IBM Security Access Manager
ID.me
Idaptive
Keeper
MicroFocus
Okta
OneLock
OneLogin
PingIdentity
PrivacyIDEA
PushCoin
Rohos
RSA SecureID Access
Sign&Go SSO (Ilex)
Thycotic
Trustelem (WALLIX)
WSO2
XTN Cognitive Security
Gandhi
GoDaddy
IPS Hosting
namecheap
opalstack
OVH
AppGate
ISL Online
SAASPASS
StrongKey
XONA
Facebook
FineFriends
Twitter
YouTube
Isosec
Linux (Debian, Ubuntu, Fedora)
Microsoft
Microsoft Edge Browser
FastMail
Gmail
Hey