Heya, glad you are taking a look around. There's lots of players offering solutions.
Here are some of the companies I see mentioned, along with my back of the envelope categorization of them; there is overlap and the categories are fuzzy, but hopefully that helps you pick and choose what to research. More info is only a google away.
OAuth/standards based solutions
* fusionauth
* auth0
* identity server/duende
Open source solutions
* ory
* keycloak
* zitadel
JavaScript focused solutions
* stytch
* propelauth
* clerk
* frontegg
* supertokens
Workforce oriented options:
* okta
* ping
* onelogin
* wso2
Hope this helps. Reach out if you'd like to chat more about FusionAuth. I'm not a co-founder (waves to Julianna) but I'm a long time employee.
Also, here are some community stories, based on interviews with folks who've used FusionAuth: https://fusionauth.io/blog/archive/category/community-story/