5150 NHC presents a very detailed system, highly applicable to solo play, for determining events in a cyberpunk, near-future setting. Events are encounters with NPCs. This is a perfect sandbox system. Although a set of events should best be determined before play and used as the game progresses, the level of detail is such that with no preparation the GM can handle a game session, although the game would be rather slowed down.
The probability if an event occurring depends on the time of day and the area in the city. Once an event occurs, there are many tables to determine the social class of the NPCs encountered (from very wealthy to criminal element), their race (human or one of five alien races), how many there are and what kind of reaction they will have when they meet the PCs. Reaction depends on the difference in social class, whether the NPCs have encountered the PCs before and other factors. Most encounters can be categorized as either combat or social.
There are also rules for what happens when the PCs are at home. Events such as burglaries and police raids are well covered.
There is also a system to determine combat and character generation, but this system can be replaced by any other SF gaming system if a rules-lite system is not your preferred way of roleplaying.
In addition to the rules for sandbox playing, there is the setting which in my view is very good. New Hope City is a city of humans, aliens, cyber enhanced individuals, low-lifes, mega corporations, mercenaries and all the other ingredients which make a very believable cyperpunk environment.
I give this game 5 stars because it is the best system to determine events I have ever seen. I even think the system could be applied to fantasy or other genres, with a bit of work from the GM.