As of this date, these are the categories and optimized-for-L5 packages available for installation from the store:
Audio & Video
Lollypop
Communication & News
Chromium
Iceweasel (i.e. Firefox browser)
Gnome Web*
Geary*
Chats*
Productivity
Geary*
Evince*
Gnome Dictionary
Games
SuperTuxKart
Gnome 2048
Gnome Chess*
Graphics & Photography
Evince*
Add-ons
GStreamer Multimedia Codecs plugins for:
ALSA
GL
GTK+3
libav plugin for GStreamer
OpenCV
plugins from the “bad” set*
plugins from the “good” set*
plugins from the “base” set*
plugins from the “ugly” set
PulseAudio
Qt5
X11 and Pango*
Developer Tools
Education & Science
Utilities
gedit*
Gnome Calculator*
PasswordSafe
Gnome Clocks*
Déjà Dup Backup Tool
Weather*
Gnome Help*
You can also use the search tool to access and install probably tens of thousands of Debian-based packages that probably won’t scale well to the screen yet, many of which can possibly just be run from the terminal anyway.
Of course, any GNU/Linux software can also be installed from the Terminal.
It’s possible to add other repositories to the PureOS store, or through the Terminal.
Edit: The asterisk next to listed packages indicates pre-installed on the L5.
Edit2: Under Add-Ons, there are also various Fonts available, and Input Sources/Methods.