QMentat helps you practice mental arithmetic. It uses arbitrary-length fixed point arithmetic, and can handle any size numbers, only limited by the size of your screen (and in the case of division with an integer result, the speed at which the number can be factored). It is also quite configurable, allowing you to tailor the questions to your needs.
Arx Libertatis is a cross-platform, open source port of Arx Fatalis, a 2002 first-person role-playing game developed by Arkane Studios. Arx Fatalis features crafting, melee and ranged combat, and a unique casting system where the player draws runes in real time to effect the desired spell. The Arx Libertatis source code is based on the publicly released Arx Fatalis sources. This does however not include the game data, so you need to obtain a copy of the original Arx Fatalis or its demo.
ZXTune is a set of portable cross-platform applications (GUI/CLI) intended to play chiptunes. It features advanced ripping possibilities that let you search for music in big data sets. Supported ZX Spectrum chiptunes formats include AY, AS0/ASC, FTC, GTR, PSC, PSG, PSM, PT1, PT2, PT3, SQT, ST1, ST3, STC, STP, TXT, TurboSound, VTX, YM, CHI, DMM, DST, PDT, SQD, STR, TF0/TFE, TFC, TFD, and COP. The Commodore64 SID format is supported. Supported PC chiptunes formats include 669, AMF, DMF, FAR, FNK, GDM, IMF, IT, LIQ, PSM, MDL, MTM, PTM, RTM, S3M, STIM, STM, STX, ULT, XM. Supported Amiga chiptune formats include DBM, EMOD, MOD, MTN, IMS, MED, OKT, PT36, SFX. Supported Atari chiptune formats include DTM, GTK, TCB. The Acorn chiptune format DTT is supported. Supported compressed formats include CHARPRES, CC3, CC4, CC4PLUS, DSQ, ESV, GAM, GAMPLUS, HRUM, HRUST1, HRUST2, LZH1, LZH2, LZS, MSP, PACK2, PCD61, PCD62, TLZ, TLZP, TRUSH. Supported archived/container formats include FDI, HOBETA, HRIP, LHA, RAW, SCL, TD0, TRD, ZXZIP, ZIP, RAR, SNA128, and Z80.