On Debian,

# Install Free Pascal compiler
sudo apt install fpc
# Install the tui ide `fp` program for editing
sudo apt install fpc-ide
# Install GUI IDE for making GUI apps
sudo apt install lazarus

For other packages, search:

# Search for other FreePascal packages
apt-cache search fp-

Some notable ones are:

fp-units-db
fp-units-math
fp-units-multimedia
fp-units-net