A tool for modifying streams, character by character.
Swap case
:L[32-][:U[32+][]#?]#?
or
:L[#L][#U]#?
or
#S
Quines
`dro;`dro;
`%rdp;`dp;
`dr[d!;]o`d!;
Truth machine
ddb'0=?u
or
ddbMN?u
Buffer the character, unbuffer it if its 0.
Concatenate stack
v'+~Y#!