Venmo (for money exchanges, especially useful for paying your friends back)
Metrolink (the app lets you buy tickets and receive updates on all trains that take you from Claremont along the Los Angeles-San Bernardino route)
Uber/Lyft (on-demand taxi services)
Yelp (food and business reviews)
Citymapper
Student Universe (cheap plane tickets and hostel reservations; travel tips and information)
Dollarbird (tracks where you are spending your money)
Cartpool (5C food and good delivery service)
5C Rideshare (find cheap Super Shuttle and other transportation trips to local airports)
Miscellaneous Tips:
Astronomy shows at the Millikan Building planetarium (on the second floor, west side) are offered regularly
Pomona's Music Department offers free 1/4 credit music lessons (voice, piano, flute, guitar, etc.!) for all ability levels which you can sign up for at the beginning of every semester. Sign-ups are in the Thatcher Music Building the first week of classes.