Mobs will bob up and down in space and zero-gravity unless they are both wearing magboots and within 1 tile of a dense object/turf.

code/game/turfs/turf.dm

@@ -130,6 +130,8 @@
 
 		else if(!istype(src, /turf/space))
 			M:inertia_dir = 0
+			var/mob/M1 = M
+			M1.make_floating(0)
 	..()
 	var/objects = 0
 	for(var/atom/A as mob|obj|turf|area in range(1))

code/modules/mob/mob.dm

@@ -679,6 +679,27 @@ note dizziness decrements automatically in the mob's Life() proc.
 	pixel_x = old_x
 	pixel_y = old_y
 
+
+//handles up-down floaty effect in space
+/mob/proc/make_floating(var/n)
+
+	floatiness = n	// store what will be new value
+
+	if(floatiness && !is_floating)
+		spawn(0)
+			floating_process()
+
+/mob/proc/floating_process()
+	is_floating = 1
+	while(floatiness)
+		var/amplitude = 2
+		var/frequency = 10
+		pixel_y = amplitude * sin(frequency * world.time)
+		sleep(1)
+	//endwhile - reset the pixel offsets to zero
+	is_floating = 0
+	pixel_y = 0
+
 /mob/Stat()
 	..()
 

code/modules/mob/mob_defines.dm

@@ -104,6 +104,8 @@
 	var/is_dizzy = 0
 	var/is_jittery = 0
 	var/jitteriness = 0//Carbon
+	var/is_floating = 0
+	var/floatiness = 0
 	var/charges = 0.0
 	var/nutrition = 400.0//Carbon
 

code/modules/mob/mob_movement.dm

@@ -402,9 +402,6 @@
 ///For moving in space
 ///Return 1 for movement 0 for none
 /mob/proc/Process_Spacemove(var/check_drift = 0)
-	//First check to see if we can do things
-	if(restrained())
-		return 0
 
 	/*
 	if(istype(src,/mob/living/carbon))
@@ -451,9 +448,19 @@
 
 	//Nothing to push off of so end here
 	if(!dense_object)
+		make_floating(1)
 		return 0
 
+	if(istype(src,/mob/living/carbon/human/))
+		if(istype(src:shoes, /obj/item/clothing/shoes/magboots) && (src:shoes.flags & NOSLIP))  //magboots + dense_object = no floaty effect
+			make_floating(0)
+		else
+			make_floating(1)
+	else
+		make_floating(1)
 
+	if(restrained()) //Check to see if we can do things
+		return 0
 
 	//Check to see if we slipped
 	if(prob(Process_Spaceslipping(5)))