Hi @dav69!
The current build comes with a few default apps pre-installed, including:
- Calls (Phone dialer)
- Chatty (SMS/MMS/XMPP app)
- Web (GNOME browser)
- Contacts
- Terminal
- Settings
- Store (PureOS software repository)
- Advanced Network Connections
- Archive Manager (manages compressed packages)
- Backups
- Calculator
- Calendar
- Camera (Dev Preview/“Millipixels”)
- Clocks (World time, alarm, stopwatch)
- Disks (graphical info about drive space, incl. attached drives)
- Document Viewer (.pdf and other formats)
- Files (directories/files browser)
- Geary (email client)
- Image Viewer
- Lollypop (stored music player)
- Maps (GNOME Maps)
- Text Editor
- Usage (info about system performance, storage, and thermals)
- Weather (GNOME Weather)
- Chess (game)
- 2048 (game)
Besides these, the Store lists a few dozen additional apps (and growing) that are made to be officially adaptive to the small screen, from the PureOS app repository (drawn from the PureOS/Debian repo), in the categories of:
- Create
- Work
- Play
- Socialize
- Learn
- Develop
- Codecs
- Fonts
- Input Sources
In addition to these, a simple search button lets you find any of thousands of other apps from the wider repo, in any category you can think of, some of which may also be adaptive to the Librem 5 (or PinePhone), but not guaranteed. Many of them may be not fully adaptive, but still usable. Others are becoming adaptive as developers start to take the new Linux phones into account, or as Purism’s developers adapt other apps along the way. All it takes to install them is tapping the “Install” button.
Some of us have been testing apps over the last year and reporting on the good ones here: List of Apps that fit and function well [Post them here.]
I encourage you to browse through those to get an idea of how things are progressing, and how the app ecosystem is shaping up.
If there’s something in particular about the Librem 5 you’re curious about, I’m sure some of us here can answer or point you in the right direction. 
Here’s a nice demo from Purism’s main site:
EDIT: Additionally, the Librem 5 has built-in settings to change scale, so an app that doesn’t normally scale well can be made to do so by just reducing it a bit.