Some things were not supposed to be Turing-complete. This is a collection of such accidents.Pokemon Yellow: The interesting point about this speedrun is the bug it exploits. Turns out the game logic itself is Turing-complete in the sense that you can rewrite the assembly itself with game actions. For example, someone turned the game into a MIDI player.
MediaWiki Templates: In MediaWiki you can define templates. Since they provide recursion, you can apparently implement lambda calculus.
1: Add ability to read email
2: Make Turing complete
3: ???
4: PROFIT!
3: Give it away and sell support for it.
FTFY. HTH.
Accidentally the whole Turing.
Not to mention that BGP, with routing policies and network delay is Turing Complete.