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).
Then your Teams client will show a menu item to switch: Click your profile picture, choose ‘About’ and then ‘Developer preview’.
Now some new feature are available. See here for a list of them. One of them is the ‘Get apps’ icon which leads you to a app directory.