The H-1B1 is a special visa for citizens of Singapore only. It is similar to an H-1B visa. Its key advantage is that it allows Singaporean citizens to avoid the H-1B quota which often runs out quickly.
The H-1B1 visa is similar to a regular H-1B in that it is available for professionals, i.e., occupations which require at least a bachelor's degree, e.g., teachers, computer programmers, engineers, accountants, etc. One of its key advantages is that it permits citizens of Singapore to get around the problems with the H-1B quota since the quota for regular H-1Bs often runs out quickly.