You can use any rule system you like to play solo:
One thing you can do is use your favorite rules and create a card driven initiative system rather like that used in "The Rules with No Name" or "Arc of Fire".
I am playing "Strange Aeons" and "No More Room in Hell" this way, and will do so for my Pulp games once I get the figures I need to get that up and running.
I explained the Strange Aeons card system here:
http://leadadventureforum.com/index.php?topic=27325.msg332411#msg332411 You can do it for any system provided you determine the goals and actions of your enemies in advance i.e. will they attack all of your figures within line of sight, will the defend certain areas (i.e. attack only if figures enter the area they are guarding), patrol and only attack if attacked and so on.
I am happy to explain it more or exchange ideas if you are interested.