Browser TM™™™ (not actually trademarked)
It's a toy implementation of a Turing Machine.. in a web browser, vanilla HTML, CSS, and JS This adds portability, it can be downloaded and run offline, and it's bare-bones, no bloat.
On a technical level, it's more aptly called a Universal Turing Machine, as described by Alan Turing. It takes an encoding of a Turing Machine (a "program" in our TM language) and an initial tape as input, and runs that Turing Machine with the tape given as input.
As of now, it's a working implementation, but it could be improved upon by writing a proper TM language compiler, tools to create a compiler for a custom TM language, ability to import and export programs, better control over TMs that have gone rogue, performance optimizations, and more.
// ignore white space <state_definition>: <state_name>: <transition_definition> <state_definition> <transition_definition>: <tape_symbol>, <state_name>, <tape_symbol>, <tape_head_direction> <transition_definition> <tape_symbol>: any single non-white space character <state_name>: [A-Za-z0-9_]+ <tape_head_direction>: [LRSlrs<>]
// reads the tape from left to right until an empty tape cell has been reached, // replacing any a's encountered with b's, and vice versa. start_state: a, start_state, b, R b, start_state, a, R _, H, _, S