Sagittarius Scheme is one of my favourite implementations. It is not the fastest, but it has a lot of packages and libraries built in, and supports both R6RS and R7RS standards.

There are two tripping points I found when installing on Ubuntu 19.10.

First, download and unpack the archive: https://bitbucket.org/ktakashi/sagittarius-scheme/downloads/

Second, follow the README and install the packages:

$ sudo apt install libgc-dev zlib1g-dev libffi-dev

Then start cmake:

$ cmake .

You may well hit a problem with missing SSL libraries, meaning you also need to install:

$ sudo apt install libssl-dev

Now the last tricky point before running cmake again - delete its cache, otherwise it does not seem to notice that the SSL libraries are now present ...

$ rm CMakeCache.txt
$ cmake .

This should finish without errors, and you can make and install:

$ make
$ sudo make install

Time to test out the new installation:

$ sagittarius --version
Sagittarius scheme shell, version 0.9.6 (x86_64-pc-linux)
$ sagittarius 
sash> (define double (lambda (n) (* 2 n)))
#<unspecified>
sash> (map double '(1 2 3 4 5))
(2 4 6 8 10)
sash> (exit)
more hello.sps
(display "Hello World") (newline)
$ sagittarius hello.sps
Hello World
$