Zymp is a Python library to design "restriction site arrays", which are compact sequences with many restriction sites.
For instance here is a 159-nucleotide sequence made with Zymp, with 49 enzyme recognition sites (out of 52 provided). That's a frequency of around 3 nucleotides per site:
PIP installation:
pip install zymp
Github Page:
https://github.com/Edinburgh-Genome-Foundry/zymp
License: MIT, Copyright Edinburgh Genome Foundry

Zymp is part of the EGF Codons synthetic biology software suite for DNA design, manufacturing and validation.