Scratch

I cannot give you a project right now that uses something like this, but you can add 'hit' sprites which can be used to detect whether the player is on a ramp or flat ground. For example if touching the ground and touching on the right then you need to slide downwards left. 

I will try and find a project which uses this but you may need to mess around with things like that:)

I guess if you don't want to use a sensor sprite, you can use different colored walls. Maybe something like this?

when flag clicked
set [xv v] to (0)
set [yv v] to (0)
forever
change x by (xv)
change y by (yv)
set [xv v] to ((xv)*(0.96)) // slow down speed (friction)
if <key [left arrow v] pressed?>
change [xv v] by (-1) //movement speed
end
if <key [right arrow v] pressed?>
change [xv v] by (1) //movement speed
end
if <touching color [#00FF00]?> //color of wall
set [xv v] to ((xv)*(-1))
end
if <touching color [#FFFF00]?> //color of normal ground
set [yv v] to (0)
else
change [yv v] by (-0.5) //speed of falling down (gravity)
end
if <touching color [#0000FF]?> //color of ramp
set [yv v] to (15) //jumping force
end
end