An example system includes a similarity module, a selection module, and a messaging module. The similarity module may receive a first set of application identifiers identifying applications downloaded or installed on at least one digital device, compare the first set of application identifiers to a second set of application identifiers identifying applications of at least one other user, generate a similarity value based on the comparison, and when the similarity value exceeds a similarity threshold, determine that the first and second sets are sufficiently similar. If the first and second sets are sufficiently similar, the selection module may determine at least one application identifier in the second set that is not in the first set. The messaging module may provide a recommendation to the first user, the recommendation including the at least one application identifier in the second set that is not in the first set.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A method comprising: receiving a first set of application identifiers identifying applications downloaded or installed on at least one digital device and associated with a first user; comparing the first set of application identifiers to a second set of application identifiers identifying applications downloaded or installed by at least one other user; generating a similarity value based on the comparison by determining similarity between the first and second sets of application identifiers; when the similarity value exceeds a similarity threshold, determining that the first and second sets are sufficiently similar; if the first and second sets are sufficiently similar: determining at least one application identifier in the second set that is not in the first set; and providing a recommendation to the first user, the recommendation including the at least one application identifier in the second set that is not in the first set. 2. The method of claim 1, wherein the at least one digital device is a mobile device. 3. The method of claim 1, wherein the recommendation further includes at least one interactive element enabling the first user to download or view information about the at least one application associated with the application identifier in the recommendation. 4. The method of claim 1, wherein receiving the first set of application identifiers identifying applications downloaded or installed by the first user on the at least one digital device comprises: identifying applications downloaded or installed on the at least one digital device; and generating the first set of application identifiers, the first set of application identifiers identifying at least one of the identified applications downloaded or installed on the digital device. 5. The method of claim 1, wherein receiving the first set of application identifiers identifying applications downloaded or installed by the first user on the at least one digital device comprises: identifying, by a Web site, applications downloaded or installed by the first user from the Web site; and generating the first set of application identifiers, the first set of application identifiers identifying at least one of the identified applications downloaded or installed by the first user. 6. The method of claim 1, wherein comparing the first set of application identifiers to the second set of application identifiers identifying applications downloaded or installed by the least one other user comprises comparing the first set of application identifiers to the second set of application identifiers identifying applications downloaded or installed by a group of other users. 7. The method of claim 6, further comprising identifying the group of other users from a plurality of groups based on at least one characteristic of the first user. 8. The method of claim 6, wherein the second set of application identifiers identifying applications downloaded or installed by the group of other users includes application identifiers identifying applications downloaded and installed by a subgroup of a larger group. 9. The method of claim 8, wherein the subgroup is at least a majority of the larger group. 10. A system comprising: a similarity module configured to receive a first set of application identifiers identifying applications downloaded or installed on at least one digital device and associated with a first user, to compare the first set of application identifiers to a second set of application identifiers identifying applications downloaded or installed by at least one other user, to generate a similarity value based on the comparison by determining similarity between the first and second sets of application identifiers, and when the similarity value exceeds a similarity threshold, to determine that the first and second sets are sufficiently similar; a selection module configured to, if the first and second sets are sufficiently similar, determine at least one application identifier in the second set that is not in the first set; and a messaging module configured to provide a recommendation to the first user, the recommendation including the at least one application identifier in the second set that is not in the first set. 11. (canceled) 12. The system of claim 10, wherein the at least one digital device is a mobile device. 13. The system of claim 10, wherein the recommendation further includes at least one interactive element enabling the first user to download or view information about the at least one application associated with the application identifier in the recommendation. 14. The system of claim 10, wherein the similarity module configured to receive the first set of application identifiers identifying applications downloaded or installed by the first user on the at least one digital device comprises the similarity module configured to: identify applications downloaded or installed, on the at least one digital device, and generate the first set of application identifiers, the first set of application identifiers identifying at least one of the identified applications downloaded or installed on the digital device. 15. The system of claim 10, wherein the similarity module configured to receive the first set of application identifiers identifying applications downloaded or installed by the first user on the at least one digital device comprises the similarity module configured to: identify, by a Web site, applications downloaded or installed by the first user from the Web site; and generate the first set of application identifiers, the first set of application identifiers identifying at least one of the identified applications downloaded or installed by the first user. 16. The system of claim 10, wherein the similarity module configured to compare the first set of application identifiers to the second set of application identifiers identifying applications downloaded or installed by the least one other user comprises the similarity module configured to compare the first set of application identifiers to the second set of application identifiers identifying applications downloaded or installed by a group of other users. 17. The system of claim 16, wherein the similarity module is further configured to identify the group of other users from a plurality of groups based on at least one characteristic of the first user. 18. The system of claim 16, wherein the second set of application identifiers identifying applications downloaded or installed by the group of other users includes application identifiers identifying applications downloaded and installed by a subgroup of a larger group. 19. The system of claim 18, wherein the subgroup is at least a majority of the larger group. 20. A non-transitory computer readable medium comprising executable instructions, the instructions being executable by a data processing device to perform a method, the method comprising: receiving a first set of application identifiers identifying applications downloaded or installed on at least one digital device and associated with a first user; comparing the first set of application identifiers to a second set of application identifiers identifying applications downloaded or installed by at least one other user; generating a similarity value based on the comparison by determining similarity between the first and second sets of application identifiers; when the similarity value exceeds a similarity threshold, determining that the first and second sets are sufficiently similar; if the first and second sets are sufficiently similar: determining at least one application identifier in the second set that is not in the first set; and providing a recommendation to the first user, the recommendation including the at least one application identifier in the second set that is not in the first set.