With the Public Developer Preview as of August 25, 2017, a new gallery to discover apps is available. Before you can use this feature, you need to switch to the ‘Developer preview”. Please read this post how you can do it. After switching you will see a new icon ‘Get apps” in the left pane.
The gallery provides a listing of all apps available in Microsoft Teams. It includes bots, tabs, connectors and compose extensions.
With a few clicks you can switch to the public developer preview for Microsoft Teams. The Public Developer Preview is a program for developers that provides early access to unreleased features (see also here). Before you can switch to the preview your central administrator must enable the sideloading of apps in the admin console of your tenant (see here).