Brimstone is a breaker program which breaks 1 firewall for a cost of 3 PWR, with no cooldown. Brimstone also has a passive effect which increases the probability of daemon reversal by 10%. Brimstone can be chosen as a starting program, or bought from some Server Terminals for 450 credits.
Brimstone's cost of 3 PWR per firewall hacked makes it one of the least efficient breaker programs — in comparison, Data Blast can break firewalls on several devices for the same PWR cost — so for Brimstone to be worthwhile, you need to get enough benefit from its passive effect. If you are often triggering daemons, then reversing an extra 10% of them may be helpful, but in practice the benefit is usually too small for it to be worth Brimstone taking up one of Incognita's program slots. Even with Faust installed, Brimstone will only reverse a daemon from Faust on average once in 50 turns, or every few missions.