Unishox is a technique for compressing short strings. This library provides for Arduino the same API as the desktop version at Unishox - Guaranteed compression for Short Strings.
To find out how Unishox works, read this article.
The following API can be used for compressing and decompressing strings or files:
int unishox_compress_simple(const char *in, long len, char *out);
int unishox_decompress_simple(const char *in, long len, char *out);
See example provided for demonstration of usage or see the documentation at https://github.com/siara-cc/Unishox for further details.
For using Unishox to store compressed data in Progmem of Arduino Uno and up, see the library at https://github.com/siara-cc/Unishox_Arduino_Progmem_lib.
The example provided with this library allows you to enter a string and see how much compression can be achieved. In general, compression utilities such as zip, gzip do not compress short strings well and often expand them. They also use lots of memory which makes them unusable in constrained environments like Arduino.