Here is a rough repost of a system I found on the internet at one time, but cannot find anymore.

Phase Combat System

The phase combat system is an optional system that can be used in place of the standard order of operations in Rifts©. This is used to make the attacks more realistic in the fact that the extra attacks a character may have would be used in the middle of the round, not at the end. Being that a melee is approximately 15 seconds, we divide the melee in into 15 separate phases at 1 second each. Everyone will roll initiative at usual and the player with the highest initiative will still goes first. During each of the phases, if the characters have attacks in the same phase as another, use initiative to find out who goes first. Other than that, the phases determine order of attacks.

	-1-	-2-	-3-	-4-	-5-	-6-	-7-	-8-	-9-	-10-	-11-	-12-	-13-	-14-	-15-
1	1
2	1							2
3	1					2					3
4	1				2				3			4
5	1			2			3			4			5
6	1			2		3			4		5			6
7	1		2		3		4			5		6		7
8	1		2		3		4		5	6		7		8
9	1		2	3		4		5	6		7		8	9
10	1		2	3		4	5		6	7		8	9		10
11	1	2		3	4	5		6	7		8	9	10		11
12	1	2		3	4	5	6		7	8	9	10		11	12
13	1	2	3	4		5	6	7	8	9	10		11	12	13
14	1	2	3	4	5	6	7	8		9	10	11	12	13	14
15	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15

As you can see, this makes more sense than having all extra attacks at the end, because it makes everything more fluid, and if two characters with the same speed are running together, they will attack at different times while being at the same place, eliminating a small problem with attacks and characters being in certain vicinities at the end of a round.

Rifts is copyright © 1983, 1987, 1988, 1990 Kevin Siembieda; © 1995 Palladium Books, All rights reserved world wide. No part of this work may be reproduced in part or whole, in any form or by any means, without permission from the publisher. All incidents, situations, institutions, governments and people are fictional and any similarity to characters or persons living or dead is strictly coincidental."

The phase combat system is copyright someone else, I imagine, and I by no means mean to step on any toes, so if you, the author see this and give me the website, I will link it all to your site. Thanks.