I use:
Acer Aspire 10" notebook (2lb 5oz, $200 at Walmart)
Linux operating system. (free download, has source code) (can dual boot without removing Windows)
GEBC Gnu Exterior Ballistics Computer (free download, has source code)
I know of no better ballistics program which has source code so it can be modified and recompiled.
I'm working on direct data transfer from my anemometer, air density sensor, and rangefinder which have serial output.
Linux Fedora can run handy accessories like:
googleearth with a GPS dongle to display current position and elevation overlaid on satellite photos.
That makes a very inexpensive long range rangefinder if the terrain has identifiable fixed objects like sparse trees. Resolution is a couple of yards.
It can also run and display various USB cameras. That has uses as a recording spotting scope or motion sensing game camera.