In accounting or invoices, à abbreviates "at a rate of": "5 apples à $1" (one dollar each). That usage is based upon the French prepositionà and has evolved into the at sign (@). Sometimes, it is part of a surname: Thomas à Kempis, Mary Anne à Beckett.
Usage in various languages
Emilian-Romagnol
À is used in Emilian to represent short stressed [a], e.g. Bolognese dialect sacàtt [saˈkatː] "sack".
À is used in Portuguese to represent a contraction of the feminine singular definite article a with the preposition a or the demonstrative aquele and its inflections and derivations (aquela, aquilo, aqueles, aquelas, aqueloutro(a), etc):
Ele foi à praia.
He went to the beach.
É igual àquela camisa que eu tinha.
It's identical to that shirt I had.
À is always unstressed, as opposed to Á and Â, which are always stressed.
Scottish Gaelic
In early orthographic descriptions of Scottish Gaelic from the 18th and 19th centuries, à is the only way to represent a long [a]; later forms of Scottish Gaelic also used the acute accent [á] to indicate a longer [a] sound.[1]
Microsoft Windows users can type an "à" by pressing Alt+133 or Alt+0224 on the numeric pad of the keyboard. "À" can be typed by pressing Alt+0192. On a Mac, you hold ⌥ Option+`, and then let go and type a. Similarly on a GNU/Linux system, where the Compose key can be configured.