Web tools
encapcalc
Encapcalc is a visual MTU and MSS calculator. Click protocol buttons and see how much they add to the frame and what the total MTU/MSS becomes.
Supports all common and many uncommon protocols from datalink to network layers: ethernet, 802.1q VLAN, IP, IPv6, TCP, IPIP, GRE and more.
Available as a standalone app from github.com/dmbaturin/encapcalc, it's a self-contained page that is easy to mirror.
BNFGen
BNFGen takes a BNF-like definition of a context-free grammar and generates a random text from it.
For rules with alternation, it allow you to choose how often each alternative is taken so that you can tweak the grammar for longer and more realistic outputs.
This is just an online version of actual bnfgen, cross-compiled to JS with BuckleScript.
OBEY
If you watched John Carpenter's They Live movie, you know what it's all about. Features most or possibly all messages seen on billboards in the movie.
For extra opression, the “next message” button is labeled “OBEY”