Example:
DOUG (DAGI) YUDOVICH is the Director of Business Information Applications for UW Physicians in Seattle. The department’s primary responsibilities range from developing enterprise-level Web-based reports and OLAP objects to developing database applications in support of various business needs for managing data. The applications vary in scope, from stop-gap applications, to bolt on tools, to mission critical–level applications that support up to 250 users.
What does that exactly mean?
Bolt on is an idiom in British English, but not in American English. (Not sure about its use in other Commonwealth countries.) The Cambridge Dictionaries Online defines it:
added to a main product, service, or plan as a smaller, extra part or feature, especially in business:
Davidow said the business would continue to make bolt-on acquisitions.
In this case, "The applications vary [...] to bolt on tools" refers to applications developed as after-market accessory tools for other applications.
Note I am not a native speaker of British English (I'm an American), but my impression is that the term "bolt on" does not imply, in British English, that the "bolt on" application runs as part of the thing it's "bolt on" to. To my American ears, "bolt on" would imply something like a plug-in or module, or something that is meant to be attached to the referent application. But I understand that's not what's meant in the British idiom. For instance, if you have an application (A) which generates hard-to-parse log files, and you developed a stand-alone application (B) for parsing the log files, even though B doesn't run as part of A, in British English you could say B was a "bolt on" to A, because the whole purpose of its existence is to make using A easier or better.