Not that many right now:

    [muep@korg ~]$ flatpak --user remote-ls flathub-beta
    Description                     Application                      Version Branch
    com.github.bilelmoussaoui.Auth… …ub.bilelmoussaoui.Authenticator         beta
    net.openra.OpenRA               net.openra.OpenRA                        beta
    org.gnome.Boxes                 org.gnome.Boxes                          beta
    org.gnome.gedit                 org.gnome.gedit                          beta
    org.godotengine.Godot           org.godotengine.Godot                    beta
    org.nextcloud.Nextcloud         org.nextcloud.Nextcloud                  beta
    [muep@korg ~]$

Which apps are available in the beta repo? 

Changes in Flathub land