BEEB Scope was a bit of fun with a relatively fast 8-bit DAC chip hung off the user port of a BBC Master Micro.
A really manky box (pics to follow, if I can find it) contained a front end with a suitable high impedance op-amp input.
The fast capture routine in the Beeb was about seven lines of 6502 code to continually read the input, allowing it to sample at about 220KHz (IIRC), which isn't bad for a 2MHz processor...
Beeb Scope screen grab
I never got round to making a really decent interface, but as I was between scopes it actually got me out of a hole a few times! A couple more screen grabs, not Compaq 5 1/4" floppies and genuine CUB monitor! This stuff belongs in a museum, not the loft.
Beeb Scope does a nice job of capturing a pulse.
Is there nothing BEEB Scope can't do?